recursive form of changing multiple spaces to one space [duplicate] - c

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Im trying to make this code recursive but for some reason it doesnt work
Im trying to write program using RECURSION to change multiple spaces to one space can anyone help ?
example "a_______b" changes to "a_b"
it is a task that im trying to do for a long time ! can anyone help ?
here i tried this but i think the design doesnt work for recursion
void text_r(char *str)
{
char *dst = str;
if(*str=='\0')return ;
*dst++ = *str;
if (isspace(*str)) {
do ++str; while (isspace(*str));
--str;
}
return text_r(str++);
}
i wrote the code without recursion but i have problem in converting it
void compress_spaces(char *str)
{
char *dst = str;
for (; *str; ++str) {
*dst++ = *str;
if (isspace(*str)) {
do ++str; while (isspace(*str));
--str;
}
}
*dst = 0;
}

Recursive version (avoiding any iterative part, like while) using the same pointer, given twice as argument
void recur(char *str, char *out) {
if (*str!=' ' || str[1]!=' ') *out++ = *str;
if (*str) recur(str+1, out);
}
Recursive version having only one param
void recur(char *str) {
static char *out = NULL;
if (out == NULL) out = str;
if (*str!=' ' || str[1]!=' ') *out++ = *str;
if (*str) recur(str+1);
}
Iterative version
void iter(char *str) {
char *out = str;
do {
if (*str!=' ' || str[1]!=' ') *out++ = *str;
} while (*str++);
}
To be called like
char str[] = " abc d e f ";
// either recursive
recur(str, str);
// or iterative
iter(str);

Not the best method but try something along these lines
char* remove_space(char *str)
{
char *dst = str;
while(*str!=' ' ||*str !='\0')
*dst++ = *str;
if (isspace(*str)) {
do ++str; while (isspace(*str));
--str;
}
return strcat(dst,remove_space(str++));
}
Idea being that you find characters and store them in a string and when you reach a space you store the first one and ignore the rest. Then you can send the new string to the function again. and you return the result concatinated with the new string
P.S. Probably the code above will not compile but it should give you a good idea on how to approach this.
Elaborating a bit:
make a function which saves all characters till a space, then ignores all consecutive spaces and sends the remaining string to a function which returns a clean string back. then it joins the two strings to make a bigger clean string.

Here's my implementation. I replace each band of multiple spaces by keeping of the last space character and make a remove that band when a nonspace character is found
void reduce(String s, int curIndex, int lastSpaceIndex)
if (lastSpaceIndex != -1)
if s[curIndex] is not a space
then replace substring from s[lastSpaceIndex, curIndex-1] by a space
else
reduce(s, curIndex+1, lastSpaceIndex);
else
if s[curIndex] is not a space
then reduce(s, curIndex+1, -1)
else
reduce(s, curIndex+1, curIndex)

Related

String Palindrome function that doesn't work as intended in C [duplicate]

What is the easiest and most efficient way to remove spaces from a string in C?
Easiest and most efficient don't usually go together…
Here's a possible solution for in-place removal:
void remove_spaces(char* s) {
char* d = s;
do {
while (*d == ' ') {
++d;
}
} while (*s++ = *d++);
}
Here's a very compact, but entirely correct version:
do while(isspace(*s)) s++; while(*d++ = *s++);
And here, just for my amusement, are code-golfed versions that aren't entirely correct, and get commenters upset.
If you can risk some undefined behavior, and never have empty strings, you can get rid of the body:
while(*(d+=!isspace(*s++)) = *s);
Heck, if by space you mean just space character:
while(*(d+=*s++!=' ')=*s);
Don't use that in production :)
As we can see from the answers posted, this is surprisingly not a trivial task. When faced with a task like this, it would seem that many programmers choose to throw common sense out the window, in order to produce the most obscure snippet they possibly can come up with.
Things to consider:
You will want to make a copy of the string, with spaces removed. Modifying the passed string is bad practice, it may be a string literal. Also, there are sometimes benefits of treating strings as immutable objects.
You cannot assume that the source string is not empty. It may contain nothing but a single null termination character.
The destination buffer can contain any uninitialized garbage when the function is called. Checking it for null termination doesn't make any sense.
Source code documentation should state that the destination buffer needs to be large enough to contain the trimmed string. Easiest way to do so is to make it as large as the untrimmed string.
The destination buffer needs to hold a null terminated string with no spaces when the function is done.
Consider if you wish to remove all white space characters or just spaces ' '.
C programming isn't a competition over who can squeeze in as many operators on a single line as possible. It is rather the opposite, a good C program contains readable code (always the single-most important quality) without sacrificing program efficiency (somewhat important).
For this reason, you get no bonus points for hiding the insertion of null termination of the destination string, by letting it be part of the copying code. Instead, make the null termination insertion explicit, to show that you haven't just managed to get it right by accident.
What I would do:
void remove_spaces (char* restrict str_trimmed, const char* restrict str_untrimmed)
{
while (*str_untrimmed != '\0')
{
if(!isspace(*str_untrimmed))
{
*str_trimmed = *str_untrimmed;
str_trimmed++;
}
str_untrimmed++;
}
*str_trimmed = '\0';
}
In this code, the source string "str_untrimmed" is left untouched, which is guaranteed by using proper const correctness. It does not crash if the source string contains nothing but a null termination. It always null terminates the destination string.
Memory allocation is left to the caller. The algorithm should only focus on doing its intended work. It removes all white spaces.
There are no subtle tricks in the code. It does not try to squeeze in as many operators as possible on a single line. It will make a very poor candidate for the IOCCC. Yet it will yield pretty much the same machine code as the more obscure one-liner versions.
When copying something, you can however optimize a bit by declaring both pointers as restrict, which is a contract between the programmer and the compiler, where the programmer guarantees that the destination and source are not the same address. This allows more efficient optimization, since the compiler can then copy straight from source to destination without temporary memory in between.
In C, you can replace some strings in-place, for example a string returned by strdup():
char *str = strdup(" a b c ");
char *write = str, *read = str;
do {
if (*read != ' ')
*write++ = *read;
} while (*read++);
printf("%s\n", str);
Other strings are read-only, for example those declared in-code. You'd have to copy those to a newly allocated area of memory and fill the copy by skipping the spaces:
char *oldstr = " a b c ";
char *newstr = malloc(strlen(oldstr)+1);
char *np = newstr, *op = oldstr;
do {
if (*op != ' ')
*np++ = *op;
} while (*op++);
printf("%s\n", newstr);
You can see why people invented other languages ;)
#include <ctype>
char * remove_spaces(char * source, char * target)
{
while(*source++ && *target)
{
if (!isspace(*source))
*target++ = *source;
}
return target;
}
Notes;
This doesn't handle Unicode.
if you are still interested, this function removes spaces from the beginning of the string, and I just had it working in my code:
void removeSpaces(char *str1)
{
char *str2;
str2=str1;
while (*str2==' ') str2++;
if (str2!=str1) memmove(str1,str2,strlen(str2)+1);
}
#include<stdio.h>
#include<string.h>
main()
{
int i=0,n;
int j=0;
char str[]=" Nar ayan singh ";
char *ptr,*ptr1;
printf("sizeof str:%ld\n",strlen(str));
while(str[i]==' ')
{
memcpy (str,str+1,strlen(str)+1);
}
printf("sizeof str:%ld\n",strlen(str));
n=strlen(str);
while(str[n]==' ' || str[n]=='\0')
n--;
str[n+1]='\0';
printf("str:%s ",str);
printf("sizeof str:%ld\n",strlen(str));
}
The easiest and most efficient way to remove spaces from a string is to simply remove the spaces from the string literal. For example, use your editor to 'find and replace' "hello world" with "helloworld", and presto!
Okay, I know that's not what you meant. Not all strings come from string literals, right? Supposing this string you want spaces removed from doesn't come from a string literal, we need to consider the source and destination of your string... We need to consider your entire algorithm, what actual problem you're trying to solve, in order to suggest the simplest and most optimal methods.
Perhaps your string comes from a file (e.g. stdin) and is bound to be written to another file (e.g. stdout). If that's the case, I would question why it ever needs to become a string in the first place. Just treat it as though it's a stream of characters, discarding the spaces as you come across them...
#include <stdio.h>
int main(void) {
for (;;) {
int c = getchar();
if (c == EOF) { break; }
if (c == ' ') { continue; }
putchar(c);
}
}
By eliminating the need for storage of a string, not only does the entire program become much, much shorter, but theoretically also much more efficient.
/* Function to remove all spaces from a given string.
https://www.geeksforgeeks.org/remove-spaces-from-a-given-string/
*/
void remove_spaces(char *str)
{
int count = 0;
for (int i = 0; str[i]; i++)
if (str[i] != ' ')
str[count++] = str[i];
str[count] = '\0';
}
Code taken from zString library
/* search for character 's' */
int zstring_search_chr(char *token,char s){
if (!token || s=='\0')
return 0;
for (;*token; token++)
if (*token == s)
return 1;
return 0;
}
char *zstring_remove_chr(char *str,const char *bad) {
char *src = str , *dst = str;
/* validate input */
if (!(str && bad))
return NULL;
while(*src)
if(zstring_search_chr(bad,*src))
src++;
else
*dst++ = *src++; /* assign first, then incement */
*dst='\0';
return str;
}
Code example
Exmaple Usage
char s[]="this is a trial string to test the function.";
char *d=" .";
printf("%s\n",zstring_remove_chr(s,d));
Example Output
thisisatrialstringtotestthefunction
Have a llok at the zString code, you may find it useful
https://github.com/fnoyanisi/zString
That's the easiest I could think of (TESTED) and it works!!
char message[50];
fgets(message, 50, stdin);
for( i = 0, j = 0; i < strlen(message); i++){
message[i-j] = message[i];
if(message[i] == ' ')
j++;
}
message[i] = '\0';
Here is the simplest thing i could think of. Note that this program uses second command line argument (argv[1]) as a line to delete whitespaces from.
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
/*The function itself with debug printing to help you trace through it.*/
char* trim(const char* str)
{
char* res = malloc(sizeof(str) + 1);
char* copy = malloc(sizeof(str) + 1);
copy = strncpy(copy, str, strlen(str) + 1);
int index = 0;
for (int i = 0; i < strlen(copy) + 1; i++) {
if (copy[i] != ' ')
{
res[index] = copy[i];
index++;
}
printf("End of iteration %d\n", i);
printf("Here is the initial line: %s\n", copy);
printf("Here is the resulting line: %s\n", res);
printf("\n");
}
return res;
}
int main(int argc, char* argv[])
{
//trim function test
const char* line = argv[1];
printf("Here is the line: %s\n", line);
char* res = malloc(sizeof(line) + 1);
res = trim(line);
printf("\nAnd here is the formatted line: %s\n", res);
return 0;
}
This is implemented in micro controller and it works, it should avoid all problems and it is not a smart way of doing it, but it will work :)
void REMOVE_SYMBOL(char* string, uint8_t symbol)
{
uint32_t size = LENGHT(string); // simple string length function, made my own, since original does not work with string of size 1
uint32_t i = 0;
uint32_t k = 0;
uint32_t loop_protection = size*size; // never goes into loop that is unbrakable
while(i<size)
{
if(string[i]==symbol)
{
k = i;
while(k<size)
{
string[k]=string[k+1];
k++;
}
}
if(string[i]!=symbol)
{
i++;
}
loop_protection--;
if(loop_protection==0)
{
i = size;
break;
}
}
}
While this is not as concise as the other answers, it is very straightforward to understand for someone new to C, adapted from the Calculix source code.
char* remove_spaces(char * buff, int len)
{
int i=-1,k=0;
while(1){
i++;
if((buff[i]=='\0')||(buff[i]=='\n')||(buff[i]=='\r')||(i==len)) break;
if((buff[i]==' ')||(buff[i]=='\t')) continue;
buff[k]=buff[i];
k++;
}
buff[k]='\0';
return buff;
}
I assume the C string is in a fixed memory, so if you replace spaces you have to shift all characters.
The easiest seems to be to create new string and iterate over the original one and copy only non space characters.
I came across a variation to this question where you need to reduce multiply spaces into one space "represent" the spaces.
This is my solution:
char str[] = "Put Your string Here.....";
int copyFrom = 0, copyTo = 0;
printf("Start String %s\n", str);
while (str[copyTo] != 0) {
if (str[copyFrom] == ' ') {
str[copyTo] = str[copyFrom];
copyFrom++;
copyTo++;
while ((str[copyFrom] == ' ') && (str[copyFrom] !='\0')) {
copyFrom++;
}
}
str[copyTo] = str[copyFrom];
if (str[copyTo] != '\0') {
copyFrom++;
copyTo++;
}
}
printf("Final String %s\n", str);
Hope it helps :-)

Selective removal of specific char in a string

Suppose I have a string that may look something like this:
"value" "some other value" "other value" "some value"
My goal is to remove the blanks selectively, like so:
"value""some other value""other value""some value"
such that the blanks remain only inside strings contained in quotes:
"some other value"
I have the following function:
void rmChar(char *str, char c)
{
char *src, *dest;
src = dest = str;
while(*src != '\0')
{
if (*src != c)
{
*dest = *src;
dest++;
}
src++;
}
*dest = '\0';
}
which removes all occurrences of char c in str and I though I should use some more conditional expressions to do the removal only when certain things happen.
Got any clues?
I just thought of doing this. Below is my program.
Note: This may not be an efficient program (bad time or space complexity), however it does what you are trying to do (if I understood your question right).
Note Also I have used malloc() in this code. You would not use it if you were changing the contents of the original string without using any other string. But as I understood from your question you were making a NEW string which contained the value of original string after removing the spaces.
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
void rmChar(char *,char, int );
int main()
{
char string[200] = "\"This is a value\" \"and another value\" \"value2 this\"";
char c;
c = '"';
printf("%s\n",string);
int len = strlen(string);
/*Pass the address of the stringi, char c, and the length of the string*/
/*Length of the string will be required for malloc() inside function rmChar()*/
rmChar(string, c, len);
return 0;
}
void rmChar(char *str,char c, int len)
{
char *dest1, *dest2;
char *src = str;
int removeFlag = 0; /* You will remove all the spaces ' ' that come after removeFlag is odd*/
dest1 = malloc(len);
dest2 = dest1;
while(*str != '\0')
{
if(*str == c)
{
removeFlag++;
if (removeFlag %2 == 0)
{
/* This is required because every 2nd time you get a " removeFlag is increased so next if is NOT true*/
*dest2 = *str;
dest2++;
}
}
if ((removeFlag % 2) == 1)
{
*dest2 = *str;
dest2++;
}
str++;
}
*dest2 = '\0';
printf("%s\n", dest1);
/* If you want to copy the string without spaces to the original string uncomment below line*/
//strcpy(src, dest1);
free(dest1);
}
You needed one more variable to use as some kind of flag which indicated after which " you need to remove spaces. Then you would use that flag in a if() statement in some way. Here int removeFlag is the flag I have used.
The loop that iterates over the string has to keep track if it is currently looking at a character inside a quoted string or not, and then use that information to only delete when appropriate.
To keep track of that information you could use an additional variable that gets updated every time there is a ".
int quoted = 0;
while (...) {
if (*src == '"') {
// set `quoted` to 1 or 0, as appropriate
...
}
// delete only if !quoted
...
}

What is wrong with this code?

As you can see below I have created a little program to concatenate 2 strings using C, as you may imagine this code doesn't work, I have already corrected it myself by using Array notation instead of pointers, and it works just fine, however I'm still not sure why is it that my code fails being almost a replica of my corrected code.
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
void concatena(char *str1, char *str2){
char *strAux;
int mover;
mover = 0;
strAux = (char *)(malloc(strlen(str1) + strlen(str2)+2));
*(strAux) = '\0';
if(str1 == '\0')
*strAux = '\0';
else
while(str1 != '\0'){
*(strAux+mover++)=*(str1++);
}
if(str2 == '\0')
*strAux = '\0';
else
while(str2 != '\0'){
*(strAux+mover++)=*(str2++);
}
strAux='\0';
str1=strAux;
printf("%s", str1);
free(strAux);
}
I´m still a C beginner (And yes, I'm aware that there are libraries like string.h, I'm asking this for academic reasons) and I have been told that char pointers and arrays are the same thing, something that confuses the heck out of me.
Any help is greatly appreciated.
The first problem I see is with this section:
if(str2 == '\0')
*strAux = '\0';
Just before this code, you've filled up strAux with the string from str1.
Then, if str2 is empty, you suddenly put a null-terminator at the beginning of strAux, eliminating all the work you've done so far!
I think what you intend is:
if(*str2 == '\0')
*(strAux+mover) = '\0';
Its the same thing again after your loop for str2, you have the code:
strAux='\0';
Again, this puts a null-terminator at the start of strAux, effectively ending the newly created string before it even gets started.
Here's how I'd re-write your code:
void concatena(char *str1, char *str2){
char *strAux;
int mover = 0;
strAux = (char *)(malloc(strlen(str1) + strlen(str2)+1)); // Changed to +1, NOT +2
*(strAux) = '\0'; // Start the string as (empty)
while(*str1 != '\0'){ // Copy the first string over.
*(strAux+mover++)=*(str1++);
}
while(*str2 != '\0'){ // Copy the second string over.
*(strAux+mover++)=*(str2++);
}
*(strAux+mover)='\0'; // End the new, combined string.
printf("%s", strAux); // Show the results.
free(strAux);
}
Accepting the same constraints, here is how I would (re)write your code. Unfortunately there is a specification shortcoming: should the concatenation occur to the first string passed? Or should a new string be created? Here are both methods:
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
char *concatena (const char *str1, const char *str2)
{
char *op, *newStr = (char*)malloc (strlen (str1) + strlen (str2) + 1);
if (!newStr)
{
fprintf (stderr, "concatena: error allocating\n");
return;
}
op = newStr; // set up output pointer
while (str1 && *str1) // copy first string
*op++ = *str1++;
while (str2 && *str2) // concatenate second string
*op++ = *str2++;
*op = '\000'; // add conventional NUL termination
return newStr;
}
void concatenb (char *str1, const char *str2)
{
char *op;
if (!str1)
{
fprintf (stderr, "concatenb: NULL string 1\n");
return;
}
op = &str1 [strlen (str1)]; // set output pointer at trailing NUL
while (str2 && *str2) // concatenate second string
*op++ = *str2++;
*op = '\000'; // add conventional NUL termination
}
strAux = (char *)(malloc(strlen(str1) + strlen(str2)+2));
2 is not required, just 1 is sufficient for the termination character.
*(strAux) = '\0';
This should be happening only at the end of all your computation. Not in between the concatenation i.e.,
while(*str1 != '\0'){ // This loops copies the first string
// ^ Notice that you need to dereference to check for the termination character.
*(strAux+mover++)=*(str1++);
}
while(*str2 != '\0'){ // This loop copies the second string
*(strAux+mover++)=*(str2++);
}
// Finally adding termination character
*(strAux+mover) = '\0'; // since with mover you are keeping track of locations.
The amount of errors in your code is disheartening. You should probably pick up a good C book and start over.
First off, there's a library function that you can use to concatenate strings:
const unsigned int len = strlen(str1) + strlen(str2) + 1;
char * dst = malloc(len);
strncat(dst, str1, len);
strncat(dst, str2, len);
Now, if you insist on doing it manually, you have to get pointers and dereferencing right:
char * d = dst;
while (*str1 != 0) *dst++ = *str1++;
while (*str2 != 0) *dst++ = *str2++;
*dst = 0;
// d now points to the beginning of the concatenated string
The two loops check if the current character in the input string is nonzero, and if so, then they copy that character to the current character in the output string, and then both input and output pointer are advanced. (This is all done in one wash by use of the postfix ++ operator.) Finally, the last character is set to zero to create a new null-terminator.
In the process we modified all three pointers dst, str1 and str2. The latter two came in as input function arguments by copy, so that's fine. For returning the concatenated string we made a copy of dst before the loop, which we can return in the end.

Writing String.trim() in C [duplicate]

This question already has answers here:
Closed 12 years ago.
Possible Duplicates:
Painless way to trim leading/trailing whitespace in C?
Trim a string in C
I was writing the String trim method in c and this is the code I came up with. I think it does the job of eliminating leading and trailing whitespaces however, I wish the code could be cleaner. Can you suggest improvements?
void trim(char *String)
{
int i=0;j=0;
char c,lastc;
while(String[i])
{
c=String[i];
if(c!=' ')
{
String[j]=c;
j++;
}
else if(lastc!= ' ')
{
String[j]=c;
j++;
}
lastc = c;
i++;
}
Does this code look clean ??
It doesn't look clean. Assuming the first character is a space, you're using lastc with an undefined value. You're leaving one space at the end (if there's a space at the end, when it's hit c will be a space and lastc won't).
You're also not terminating the string. Assuming you fix the uninitialized lastc problem, you'll transform " abc" to "abcbc", since it's not being shortened at any point.
The code also collapses multiple spaces inside the string. This isn't what you described; is it desired behavior?
It often makes your code more readable if you make judicious use of the standard library functions - for example, isspace() and memmove() are particularly useful here:
#include <string.h>
#include <ctype.h>
void trim(char *str)
{
char *start, *end;
/* Find first non-whitespace */
for (start = str; *start; start++)
{
if (!isspace((unsigned char)start[0]))
break;
}
/* Find start of last all-whitespace */
for (end = start + strlen(start); end > start + 1; end--)
{
if (!isspace((unsigned char)end[-1]))
break;
}
*end = 0; /* Truncate last whitespace */
/* Shift from "start" to the beginning of the string */
if (start > str)
memmove(str, start, (end - start) + 1);
}
There's several problems with that code. It only checks for space. Not tabs or newlines. You are copying the entire non-whitespace part of the string. And you are using lastc before setting it.
Here's an alternate version (compiled but not tested):
char *trim(char *string)
{
char *start;
int len = strlen(string);
int i;
/* Find the first non whitespace char */
for (i = 0; i < len; i++) {
if (! isspace(string[i])) {
break;
}
}
if (i == len) {
/* string is all whitespace */
return NULL;
}
start = &string[i];
/* Remove trailing white space */
for (i = len; i > 0; i--) {
if (isspace(string[i])) {
string[i] = '\0';
} else {
break;
}
}
return start;
}
There are some problems: lastc could be used uninitialized. And you could make use of a for loop instead of a while loop, for example. Furthermore, trim/strip functions usually replace spaces, tabs and newlines.
Here's a solution using pointers that I wrote quite a while ago:
void trim(char *str)
{
char *ptr = str;
while(*ptr == ' ' || *ptr == '\t' || *ptr == '\r' || *ptr == '\n') ++ptr;
char *end = ptr;
while(*end) ++end;
if(end > ptr)
{
for(--end; end >= ptr && (*end == ' ' || *end == '\t' || *end == '\r' || *end == '\n'); --end);
}
memmove(str, ptr, end-ptr);
str[end-ptr] = 0;
}
Here is my solution.
Short, simple, clean, commented, and lightly tested.
It uses the "isspace" classification function, so you can easily change your definition of "white space" to be trimmed.
void trim(char* String)
{
int dest;
int src=0;
int len = strlen(String);
// Advance src to the first non-whitespace character.
while(isspace(String[src])) src++;
// Copy the string to the "front" of the buffer
for(dest=0; src<len; dest++, src++)
{
String[dest] = String[src];
}
// Working backwards, set all trailing spaces to NULL.
for(dest=len-1; isspace(String[dest]); --dest)
{
String[dest] = '\0';
}
}
Instead of comparing a character with the space character ' ', I'd use the "isspace" function, which I believe is defined in ctype.h.
I don't know about clean, but I find it hard to follow. If I needed to do this I'd initially think of it in two phases:
Figure out how many characters to drop from the beginning, then memmove the rest of the string (including the null terminator) to the start address. (You might not need the memmove if you are allowed to return a different start pointer, but if so you need to be very careful with memory hygiene.)
Figure out how many characters to drop from the (new) end and set a new null terminator there.
I might then look more closely at a one-pass solution like you seem to be trying to implement, but only if there was a speed problem.
By the way, you probably want to use isspace() rather than checking only for space.

Remove spaces from a string in C

What is the easiest and most efficient way to remove spaces from a string in C?
Easiest and most efficient don't usually go together…
Here's a possible solution for in-place removal:
void remove_spaces(char* s) {
char* d = s;
do {
while (*d == ' ') {
++d;
}
} while (*s++ = *d++);
}
Here's a very compact, but entirely correct version:
do while(isspace(*s)) s++; while(*d++ = *s++);
And here, just for my amusement, are code-golfed versions that aren't entirely correct, and get commenters upset.
If you can risk some undefined behavior, and never have empty strings, you can get rid of the body:
while(*(d+=!isspace(*s++)) = *s);
Heck, if by space you mean just space character:
while(*(d+=*s++!=' ')=*s);
Don't use that in production :)
As we can see from the answers posted, this is surprisingly not a trivial task. When faced with a task like this, it would seem that many programmers choose to throw common sense out the window, in order to produce the most obscure snippet they possibly can come up with.
Things to consider:
You will want to make a copy of the string, with spaces removed. Modifying the passed string is bad practice, it may be a string literal. Also, there are sometimes benefits of treating strings as immutable objects.
You cannot assume that the source string is not empty. It may contain nothing but a single null termination character.
The destination buffer can contain any uninitialized garbage when the function is called. Checking it for null termination doesn't make any sense.
Source code documentation should state that the destination buffer needs to be large enough to contain the trimmed string. Easiest way to do so is to make it as large as the untrimmed string.
The destination buffer needs to hold a null terminated string with no spaces when the function is done.
Consider if you wish to remove all white space characters or just spaces ' '.
C programming isn't a competition over who can squeeze in as many operators on a single line as possible. It is rather the opposite, a good C program contains readable code (always the single-most important quality) without sacrificing program efficiency (somewhat important).
For this reason, you get no bonus points for hiding the insertion of null termination of the destination string, by letting it be part of the copying code. Instead, make the null termination insertion explicit, to show that you haven't just managed to get it right by accident.
What I would do:
void remove_spaces (char* restrict str_trimmed, const char* restrict str_untrimmed)
{
while (*str_untrimmed != '\0')
{
if(!isspace(*str_untrimmed))
{
*str_trimmed = *str_untrimmed;
str_trimmed++;
}
str_untrimmed++;
}
*str_trimmed = '\0';
}
In this code, the source string "str_untrimmed" is left untouched, which is guaranteed by using proper const correctness. It does not crash if the source string contains nothing but a null termination. It always null terminates the destination string.
Memory allocation is left to the caller. The algorithm should only focus on doing its intended work. It removes all white spaces.
There are no subtle tricks in the code. It does not try to squeeze in as many operators as possible on a single line. It will make a very poor candidate for the IOCCC. Yet it will yield pretty much the same machine code as the more obscure one-liner versions.
When copying something, you can however optimize a bit by declaring both pointers as restrict, which is a contract between the programmer and the compiler, where the programmer guarantees that the destination and source are not the same address. This allows more efficient optimization, since the compiler can then copy straight from source to destination without temporary memory in between.
In C, you can replace some strings in-place, for example a string returned by strdup():
char *str = strdup(" a b c ");
char *write = str, *read = str;
do {
if (*read != ' ')
*write++ = *read;
} while (*read++);
printf("%s\n", str);
Other strings are read-only, for example those declared in-code. You'd have to copy those to a newly allocated area of memory and fill the copy by skipping the spaces:
char *oldstr = " a b c ";
char *newstr = malloc(strlen(oldstr)+1);
char *np = newstr, *op = oldstr;
do {
if (*op != ' ')
*np++ = *op;
} while (*op++);
printf("%s\n", newstr);
You can see why people invented other languages ;)
#include <ctype>
char * remove_spaces(char * source, char * target)
{
while(*source++ && *target)
{
if (!isspace(*source))
*target++ = *source;
}
return target;
}
Notes;
This doesn't handle Unicode.
if you are still interested, this function removes spaces from the beginning of the string, and I just had it working in my code:
void removeSpaces(char *str1)
{
char *str2;
str2=str1;
while (*str2==' ') str2++;
if (str2!=str1) memmove(str1,str2,strlen(str2)+1);
}
#include<stdio.h>
#include<string.h>
main()
{
int i=0,n;
int j=0;
char str[]=" Nar ayan singh ";
char *ptr,*ptr1;
printf("sizeof str:%ld\n",strlen(str));
while(str[i]==' ')
{
memcpy (str,str+1,strlen(str)+1);
}
printf("sizeof str:%ld\n",strlen(str));
n=strlen(str);
while(str[n]==' ' || str[n]=='\0')
n--;
str[n+1]='\0';
printf("str:%s ",str);
printf("sizeof str:%ld\n",strlen(str));
}
The easiest and most efficient way to remove spaces from a string is to simply remove the spaces from the string literal. For example, use your editor to 'find and replace' "hello world" with "helloworld", and presto!
Okay, I know that's not what you meant. Not all strings come from string literals, right? Supposing this string you want spaces removed from doesn't come from a string literal, we need to consider the source and destination of your string... We need to consider your entire algorithm, what actual problem you're trying to solve, in order to suggest the simplest and most optimal methods.
Perhaps your string comes from a file (e.g. stdin) and is bound to be written to another file (e.g. stdout). If that's the case, I would question why it ever needs to become a string in the first place. Just treat it as though it's a stream of characters, discarding the spaces as you come across them...
#include <stdio.h>
int main(void) {
for (;;) {
int c = getchar();
if (c == EOF) { break; }
if (c == ' ') { continue; }
putchar(c);
}
}
By eliminating the need for storage of a string, not only does the entire program become much, much shorter, but theoretically also much more efficient.
/* Function to remove all spaces from a given string.
https://www.geeksforgeeks.org/remove-spaces-from-a-given-string/
*/
void remove_spaces(char *str)
{
int count = 0;
for (int i = 0; str[i]; i++)
if (str[i] != ' ')
str[count++] = str[i];
str[count] = '\0';
}
Code taken from zString library
/* search for character 's' */
int zstring_search_chr(char *token,char s){
if (!token || s=='\0')
return 0;
for (;*token; token++)
if (*token == s)
return 1;
return 0;
}
char *zstring_remove_chr(char *str,const char *bad) {
char *src = str , *dst = str;
/* validate input */
if (!(str && bad))
return NULL;
while(*src)
if(zstring_search_chr(bad,*src))
src++;
else
*dst++ = *src++; /* assign first, then incement */
*dst='\0';
return str;
}
Code example
Exmaple Usage
char s[]="this is a trial string to test the function.";
char *d=" .";
printf("%s\n",zstring_remove_chr(s,d));
Example Output
thisisatrialstringtotestthefunction
Have a llok at the zString code, you may find it useful
https://github.com/fnoyanisi/zString
That's the easiest I could think of (TESTED) and it works!!
char message[50];
fgets(message, 50, stdin);
for( i = 0, j = 0; i < strlen(message); i++){
message[i-j] = message[i];
if(message[i] == ' ')
j++;
}
message[i] = '\0';
Here is the simplest thing i could think of. Note that this program uses second command line argument (argv[1]) as a line to delete whitespaces from.
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
/*The function itself with debug printing to help you trace through it.*/
char* trim(const char* str)
{
char* res = malloc(sizeof(str) + 1);
char* copy = malloc(sizeof(str) + 1);
copy = strncpy(copy, str, strlen(str) + 1);
int index = 0;
for (int i = 0; i < strlen(copy) + 1; i++) {
if (copy[i] != ' ')
{
res[index] = copy[i];
index++;
}
printf("End of iteration %d\n", i);
printf("Here is the initial line: %s\n", copy);
printf("Here is the resulting line: %s\n", res);
printf("\n");
}
return res;
}
int main(int argc, char* argv[])
{
//trim function test
const char* line = argv[1];
printf("Here is the line: %s\n", line);
char* res = malloc(sizeof(line) + 1);
res = trim(line);
printf("\nAnd here is the formatted line: %s\n", res);
return 0;
}
This is implemented in micro controller and it works, it should avoid all problems and it is not a smart way of doing it, but it will work :)
void REMOVE_SYMBOL(char* string, uint8_t symbol)
{
uint32_t size = LENGHT(string); // simple string length function, made my own, since original does not work with string of size 1
uint32_t i = 0;
uint32_t k = 0;
uint32_t loop_protection = size*size; // never goes into loop that is unbrakable
while(i<size)
{
if(string[i]==symbol)
{
k = i;
while(k<size)
{
string[k]=string[k+1];
k++;
}
}
if(string[i]!=symbol)
{
i++;
}
loop_protection--;
if(loop_protection==0)
{
i = size;
break;
}
}
}
While this is not as concise as the other answers, it is very straightforward to understand for someone new to C, adapted from the Calculix source code.
char* remove_spaces(char * buff, int len)
{
int i=-1,k=0;
while(1){
i++;
if((buff[i]=='\0')||(buff[i]=='\n')||(buff[i]=='\r')||(i==len)) break;
if((buff[i]==' ')||(buff[i]=='\t')) continue;
buff[k]=buff[i];
k++;
}
buff[k]='\0';
return buff;
}
I assume the C string is in a fixed memory, so if you replace spaces you have to shift all characters.
The easiest seems to be to create new string and iterate over the original one and copy only non space characters.
I came across a variation to this question where you need to reduce multiply spaces into one space "represent" the spaces.
This is my solution:
char str[] = "Put Your string Here.....";
int copyFrom = 0, copyTo = 0;
printf("Start String %s\n", str);
while (str[copyTo] != 0) {
if (str[copyFrom] == ' ') {
str[copyTo] = str[copyFrom];
copyFrom++;
copyTo++;
while ((str[copyFrom] == ' ') && (str[copyFrom] !='\0')) {
copyFrom++;
}
}
str[copyTo] = str[copyFrom];
if (str[copyTo] != '\0') {
copyFrom++;
copyTo++;
}
}
printf("Final String %s\n", str);
Hope it helps :-)

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