I did a simple program that splits a string in substrings, using the whitespace as a split reference. The program was working as expected, so I've decided to put this code inside a function that is called "substring_whitespace".This function return a size_t value which is the number of substring's. The function arguments are char* buffer[] and char* string. Both are pointers, the first will store the substring's, and the second is the string that'll be splited.
Here is the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
size_t substring_whitespace(char* buffer[],char* string) {
size_t initial_string_size = strlen(string) + 1;
char actual_string[initial_string_size];
char strings[initial_string_size][initial_string_size];
strcpy(actual_string,string);
size_t c = 0;
for(; c<initial_string_size; c++) {
size_t first_whitespace_index = strcspn(actual_string," ");
char substring[first_whitespace_index];
for(size_t d = 0; d<=first_whitespace_index; d++) {
if(d == first_whitespace_index)
substring[first_whitespace_index] = 0;
else
substring[d] = actual_string[d];
}
size_t actual_string_length = strlen(actual_string);
size_t new_actual_string_length = (actual_string_length - first_whitespace_index) + 1;
char new_actual_string[new_actual_string_length];
for(size_t d = 0,i = first_whitespace_index + 1; i<=actual_string_length + 1; i++,d++) {
if(i == actual_string_length)
new_actual_string[d] = 0;
else
new_actual_string[d] = actual_string[i];
}
strcpy(actual_string,new_actual_string);
strcpy(strings[c],substring);
buffer[c] = strings[c];
if(new_actual_string_length == 1)
break;
}
return ++c;\
}
int main() {
char string[1000];
fgets(string,sizeof(string)/sizeof(string[0]),stdin);
string[strcspn(string,"\n")] = 0;
char* buffer[strlen(string) + 1];
size_t buffer_length = substring_whitespace(buffer,string);
for(int d = 0; d<buffer_length; d++) {
printf("\n%s",buffer[d]);
}
}
After I test, the results were not as expected, so during my debug I detect that the char were being changed after get off the function by pointer. This behavior is only detectable if I try to print the buffer strings in the main.
strings is a local variable whose lifetime ends when the function returns. The easiest fix is to copy the string when assigning a value buffer[c]:
buffer[c] = strdup(strings[c]);
Another option is to change the design and return an array of ranges relative to your input string. For example struct range { char *s; size_t len; };, and if string is "hello world" the function could return [{string, 5}, {string+6, 5}].
Related
#include <stdio .h>
#include <stdlib .h>
int main(){
char text1 [N] ;
char reverse [N] ;
char* txtptr = text1 ;
char* revtxtptr = reverse ;
int N;
printf (”\n Enter any text here : ”) ;
scanf(”%s”, text1);
while(N> 0){
txtptr --;
*revtxtptr = *txtptr ;
revtxtptr++;
}
*revtxtptr = ’\0’;
printf (”The reverse text is : %s \n” , reverse) ;
return 0;
}
I want to see here output the reverse form of the input.
Something like
input:
CLEARLY
output:
YLRAELC
Could you help me to fix my fault?
Here are corrections to your code:
You have spaces before the .h> in the #include lines.
You should limit the size of the buffers.
N is not initialized.
N is not being decremented.
txtptr is not being placed at the end of the C string, but it is being decremented in the while loop.
scanf is not limited to the size of the buffer(s) minus 1.
You need to either find the size of the string using strlen or walk the string until you find '\0'. (forward direction instead)
You use the wrong double-quotes and single quotes ("smart" quotes)
Here is a safe code that will reverse the input array (not in-place):
#include <stdio.h>
#include <stdlib.h>
#define MAXSTR 255
#define STR_HELPER(x) #x
#define STR(x) STR_HELPER(x)
int main() {
char text1[MAXSTR + 1];
char revbuf[MAXSTR + 1];
char* txtptr = text1;
char* reverse = revbuf + MAXSTR;
printf("\nEnter any text here : ");
scanf("%" STR(MAXSTR) "s", text1);
*reverse = '\0';
while(*txtptr) {
*--reverse = *txtptr++;
}
printf ("The reverse text is : %s \n" , reverse) ;
return 0;
}
Here you have an example function for int array.
int *reverseINTarray(int *array, size_t size)
{
int *end, *wrk = array;
if(array && size > 1)
{
end = array + size - 1;
while(end > wrk)
{
int tmp = *wrk;
*wrk++ = *end;
*end-- = tmp;
}
}
return array;
}
or
int *reverseINTarray(const int *src, int *dest, size_t size)
{
int *wrk = dest;
if(src && dest && size)
{
wrk += size - 1;
while(size--)
{
*wrk-- = *src++;
}
}
return dest;
}
Your "swap two bytes" logic is ... simply ... wrong. Does this give you any ideas?
char temp;
temp = *chartxtptr;
*chartxtptr = *txtptr;
*txtptr = temp;
You can't "swap" any two bytes without using a temporary to hold the byte that is about to be replaced.
I am working to learn C using Kochan's Programming in C 4th edition. problem 9.7 the goal is to insert a string of characters into another array. I am supposed to write a function to accomplish this. I have two problems.
When I have the algorithm print the result as it goes through the if statements, it produces the desired output, however when I change it to an %s, I only get a partial output. My hunch is that a null character is being placed where i do not want it, but I simply cannot see it.
To see what was happening, I added a printf that would track the letter and the array space it was occupying. I was surprised to see that the first letter was not 0, but was blank, and the next letter was assigned the 0. Any insight into this would be appreciated.
The funtion of interest is "insertString".
#include <stdio.h>
#include <stdbool.h>
char x[] = {"the wrong son was shot that day"};
char text[] = {"per"};
int countString (char x[])
{
int counter, z;
for (counter = 0; x[counter] != '\0'; ++counter)
z = counter+1;
return z;
}
void insertString (char text[],char x[],int n) //source, text to input, where
{
int count, clock, i = countString(text), q = countString(x);
int counter = 0;
char y[i + q];
for(count = 0; x[count] != '\0'; ++count){
if (count < n){
y[count] = x[count];
printf("%c %i", y[count], count); //The integer call is just to put a number next to the
//letter. This is where my second issue is shown.
}
else if (counter <= i){
y[count] = text[counter];
++counter;
printf("%c", y[count]);
}
else{
y[count]= x[count - counter];
printf("%c", y[count]);
}
}
printf("\n\n");
y[count-counter] = '\0';
printf("%s", y);
}
int main (void)
{
void insertString(char text[], char x[], int i);
int countString(char x[]);
int i;
insertString(text, x, 10);
return 0;
}
10 out of 10 times I post here it is because im doing something dumb, so I use SO as an absolute last resort if i am getting into the territory of just randomly trying stuff with no methodology. Thanks for your patience in advance.
Your condition is wrong in the for. It should be x[count - counter] != '\0'
In the second condition use just < to avoid overindexing. (else if (counter < i))
You put the terminating NULL char at wrong place. You should do this: y[count] = '\0'
printf inside a string routine like this is fine for debugging, but it's a poor way to write a general-purpose function because it makes it impossible to use its output for further programmatic manipulation. It can also make it difficult to reason about how the state of the function interacts in unpredictable ways with the state of the printed data.
I assume you haven't learned about dynamic memory allocation which is a prerequisite to returning strings from functions. You can inline the function logic into main or printf only at the end of the function in the meantime.
Adding to this point, a void function would need to reallocate space in the string to insert into and would be in-place. This seems likely less generally useful than allocating a new string to hold the result.
Using global variables like char x[] when there's no need is poor practice. It's better to put those strings scoped to main. Since your function can access these variables in addition to its parameters, confusion can ensue when scope and encapsulation is breached.
Use consistent formatting and avoid variable names like q that mean virtually nothing. Instead of adding comments to explain poor var names:
void insertString (char text[],char x[],int n) //source, text to input, where
You can simply name the variables exactly what they represent:
void insertString(char *dest, char *source, int add_index)
Also, now that you've mastered countString, you can abstract this by calling the builtin strlen.
Be sure to allocate enough space in buffers: char y[i + q]; should be y[i+q+1] to allow room for the null terminator '\0'.
As for the logic, I think it's easier to break into three loops without conditions instead of one loop with conditions. This makes it easier to break the problem down into the three constituent steps:
Add everything up until add_index from the dest string to the result.
Add everything in the source string to the result.
Add everything after add_index from the dest string to the result.
Using this approach, all that's left is figuring out how to map the indexes appropriately. Here it is in code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *insert_string(char *dest, char *source, int add_index) {
int source_len = strlen(source);
int dest_len = strlen(dest);
int result_size = source_len + dest_len + 1;
char *result = malloc(result_size);
for (int i = 0; i < add_index; i++) {
result[i] = dest[i];
}
for (int i = 0; i < source_len; i++) {
result[i+add_index] = source[i];
}
for (int i = add_index; i < dest_len; i++) {
result[i+add_index] = dest[i];
}
result[result_size-1] = '\0';
return result;
}
int main(void) {
char *result = insert_string("hello world", "cruel ", 6);
printf("%s\n", result);
free(result);
return 0;
}
Although this is likely for instructional purposes, these operations can be abstracted further using builtin string functions like strncpy and sprintf.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *insert_string(char *dest, char *source, int add_index) {
int result_size = strlen(dest) + strlen(source) + 1;
char *result = malloc(result_size);
char pre[add_index+1];
pre[add_index] = '\0';
strncpy(pre, dest, add_index);
sprintf(result, "%s%s%s", pre, source, dest + add_index);
return result;
}
int main(void) {
char *result = insert_string("hello world", "cruel ", 6);
printf("%s\n", result);
free(result);
return 0;
}
Doing this in-place is more straightforward. Since the result already has the prefix, you can copy the destination postfix to create a source-sized gap in the middle and then overwrite the gap using the source string. It's up to the caller to make sure that the destination buffer is large enough to hold the insertion.
#include <stdio.h>
#include <string.h>
void insert_string(char *dest, char *source, int add_index) {
int source_len = strlen(source);
int dest_len = strlen(dest);
for (int i = add_index; i < dest_len; i++) {
dest[i+add_index] = dest[i];
}
for (int i = 0; i < source_len; i++) {
dest[i+add_index] = source[i];
}
}
int main(void) {
// allocate extra space in the string to hold the insertion
char greeting[32] = "hello world";
insert_string(greeting, "cruel ", 6);
printf("%s\n", greeting);
return 0;
}
A note of caution: none of these functions handle errors at all, so they're unsafe. Correct functions should check that the add_index falls within the bounds of the dest string. This is an exercise for the reader.
The original exercise is here:
Your function is not doing it. You need to insert the string into another string not to create a new one with both mixed. You can do it this way of course and then copy it into the original one - but it is the most uneficient way to archive it (memory & timewise).
Use the correct types.
size_t mystrlen(const char *str)
{
const char *end = str;
while(*end++);
return end - str - 1;
}
char *strinsert(char *dest, size_t pos, const char *istr)
{
char *temp = dest, *work;
size_t ilen = mystrlen(istr);
size_t nmove;
while(*temp) temp++;
nmove = temp - dest - pos + 1;
work = temp;
temp += ilen;
while(nmove--) *temp-- = *work--;
work = dest + pos;
while(*istr) *work++ = *istr++;
return dest;
}
int main()
{
char dest[128] = "0123456789012345678901234567890123456789";
printf("%s", strinsert(dest, 7, "ABCD"));
}
https://godbolt.org/z/KMnLU2
I'm trying to count the number of indexes of an undefined char array which is used as a parameter in the function.
I am already aware that if my array was fixed I can use "sizeof", which isn't the case here.
Attempt:
int counting(char *name3) {
int count = 0;
int i;
//I have no idea what to put as my condition nor do I believe
//I am approaching this situation correctly...
for (i = 0; i < sizeof(name3); i++) {
if (name3[i] != '\0') {
count++;
}
}
return count;
}
Then if it is run by the following code
int main(void) {
char *name = "Lovely";
int x = counting(name);
printf ("The value of x = %d", x);
Prints: The value of x = 0
Any help or pointers would be amazing. Thank you in advance.
In C, Every string ends with '\0' (Null Character)
You can iterate until you meet the Null Character
The example code would be like this
char* name = "Some Name";
int len = 0;
while (name[len] != '\0') {
len++;
}
Also, if it is a char pointer, not char array, sizeof(char*) will always return 4 in 32-bit application and return 8 in 64-bit application (the size of the 'pointer' itself - the memory address size)
#include <stdio.h>
int main()
{
int i=0;
char *name = "pritesh";
for(i=0;;i++)
{
if(name[i] == '\0')
{
break;
}
}
printf("%d", i);
return 0;
}
This should work
note: this might be syntactically incorrect as I have not had my hands on c since a long time
The function char *my(char *s, int n) takes a string s and shifts the characters of s by n places, causing the characters to wrap around the string.
For example, given the string "This is my Apple!" , a shift of n = 2 will result in
String1: "Th"
String2: "is is my Apple!"
if n<0 it will shift in negative direction.
You can just use printf to split a string. If you want the result in a char *, you have to allocate some memory and use sprintf instead.
Here is a example using sprintfand memory allocation to return a char *.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *shift(char *string, int n)
{
int len = strlen(string);
char *shiftedString = malloc(len + 1);
n %= len; // in case you shift over string length
if (n < 0) n += len; // backward shift
sprintf(shiftedString, "%s%*.*s", string + n, n, n, string);
return shiftedString;
}
int main()
{
char *result = shift("This is my Apple!", 2);
printf("shifted string : %s\n", result);
free(result);
return 0;
}
the string is actually a char-array char[]
you could use the strlen function in combination with a for loop like so.
You can put that in a function thus creating your own function that would shift letters based on input N.
#include <stdio.h>
#include <string.h>
int main()
{
char string[] = "This is my Apple!";
//Initialize "n" before initializing the string variables.
int n = 2;
int len = strlen(string);
char string1[n];
char string2[len - n];
for(int i = 0;i<len;i++){
if(i<n){
string1[i]=string[i];
}else{
string2[i-n]=string[i];
}
}
printf("string = %s\n",string);
printf("string1 = %s\n",string1);
printf("string2 = %s\n",string2);
return 0;
}
I have a variable length string where each character represents a hex digit. I could iterate through the characters and use a case statement to convert it to hex but I feel like there has to be a standard library function that will handle this. Is there any such thing?
Example of what I want to do. "17bf59c" -> int intarray[7] = { 1, 7, 0xb, 0xf, 5, 9, 0xc}
No, there's no such function, probably because (and now I'm guessing, I'm not a C standard library architect by a long stretch) it's something that's quite easy to put together from existing functions. Here's one way of doing it decently:
int * string_to_int_array(const char *string, size_t length)
{
int *out = malloc(length * sizeof *out);
if(out != NULL)
{
size_t i;
for(i = 0; i < length; i++)
{
const char here = tolower(string[i]);
out[i] = (here <= '9') ? (here - '\0') : (10 + (here - 'a'));
}
}
return out;
}
Note: the above is untested.
Also note things that maybe aren't obvious, but still subtly important (in my opinion):
Use const for pointer arguments that are treated as "read only" by the function.
Don't repeat the type that out is pointing at, use sizeof *out.
Don't cast the return value of malloc() in C.
Check that malloc() succeeded before using the memory.
Don't hard-code ASCII values, use character constants.
The above still assumes an encoding where 'a'..'f' are contigous, and would likely break on e.g. EBCDIC. You get what you pay for, sometimes. :)
using strtol
void to_int_array (int *dst, const char *hexs)
{
char buf[2] = {0};
char c;
while ((c = *hexs++)) {
buf[0] = c;
*dst++ = strtol(buf,NULL,16);
}
}
Here's another version that allows you to pass in the output array. Most of the time, you don't need to malloc, and that's expensive. A stack variable is typically fine, and you know the output is never going to be bigger than your input. You can still pass in an allocated array, if it's too big, or you need to pass it back up.
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
/* str of length len is parsed to individual ints into output
* length of output needs to be at least len.
* returns number of parsed elements. Maybe shorter if there
* are invalid characters in str.
*/
int string_to_array(const char *str, int *output)
{
int *out = output;
for (; *str; str++) {
if (isxdigit(*str & 0xff)) {
char ch = tolower(*str & 0xff);
*out++ = (ch >= 'a' && ch <= 'z') ? ch - 'a' + 10 : ch - '0';
}
}
return out - output;
}
int main(void)
{
int values[10];
int len = string_to_array("17bzzf59c", values);
int i = 0;
for (i = 0; i < len; i++)
printf("%x ", values[i]);
printf("\n");
return EXIT_SUCCESS;
}
#include <stdio.h>
int main(){
char data[] = "17bf59c";
const int len = sizeof(data)/sizeof(char)-1;
int i,value[sizeof(data)/sizeof(char)-1];
for(i=0;i<len;++i)
sscanf(data+i, "%1x",value + i);
for(i=0;i<len;++i)
printf("0x%x\n", value[i]);
return 0;
}