I'm trying to make a word counter program and want to dynamically allocate memory for the string without extra space. Here's my code so far:
#include <stdio.h>
#include <stdlib.h>
char *strmalloc(char *string);
char *user_input = NULL;
int main(void) {
printf("Enter a sentence to find out the number of words: ");
strmalloc(user_input);
printf("You entered %s", user_input);
return 0;
}
char *strmalloc(char *string) {
char *tmp = NULL;
size_t size = 0, index = 0;
int ch;
while ((ch = getchar()) != '\n' && ch != EOF) {
if (size <= index) {
size += 1;
tmp = realloc(string, size);
if (!tmp) {
free(string);
string = NULL;
break;
}
string = tmp;
}
string[index++] = ch;
}
return string;
}
Here's the output:
Enter a sentence to find out the number of words: Testing program
You entered (null)
Process finished with exit code 0
I thought that in the while loop, I reallocate 1 byte of memory until the string fits just right? What am I doing wrong?
In your functiuon:
char *strmalloc(char *string) { ===> char *strmalloc(char **string) {
tmp = realloc(string, size); ===> tmp = realloc(*string, size);
string = NULL; ===> *string = NULL;
string = tmp; ===> *string = tmp;
string[index++] = ch; ===> (*string)[index++] = ch;
return string; ===> return *string;
In the calling function:
strmalloc(user_input); ===> strmalloc(&user_input);
Related
I'm building a word counter program. To achieve this, I was thinking about saving the string the user inputted, and using strtok() to split the sentence with space as the delimiter. But first I want to allocate enough memory for each word. Let's say the sentence is "Hello World". I've already dynamically allocated memory for the string itself. Now I want to split Hello World into 2 strings, "Hello" and "World". My goal is to allocate enough memory so that there's not too much empty space but I also don't want to allocate too little space. Here is my code so far:
#include <stdio.h>
#include <stdlib.h>
char *strmalloc(char **string);
char *user_input = NULL;
char *word_array[];
int main(void) {
printf("Enter a sentence to find out the number of words: ");
user_input = strmalloc(&user_input);
return 0;
}
char *strmalloc(char **string) {
char *tmp = NULL;
size_t size = 0, index = 0;
int ch;
while ((ch = getchar()) != '\n' && ch != EOF) {
if (size <= index) {
size += 1;
tmp = realloc(*string, size);
if (!tmp) {
free(*string);
string = NULL;
break;
}
*string = tmp;
}
(*string)[index++] = ch;
}
return *string;
}
How would I go about doing this? Should I do the splitting first or allocate the space required for the array first?
You can count words without splitting the sentence, here is an example :
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
// Change this to change the separator characters
static inline char isSeparator(char ch) { return isspace(ch) || ispunct(ch); }
char * jumpSeparator(char *string) {
while(string[0] && isSeparator(string[0])) string++;
return string;
}
char * findEndOfWord(char *string) {
while (string[0] && !isSeparator(string[0])) string++;
return string;
}
int countWords(char *string) {
char * ptr = jumpSeparator(string);
if (strlen(ptr) == 0) return 0;
int count = 1;
while((ptr = findEndOfWord(ptr)) && ptr[0]) {
ptr = jumpSeparator(ptr);
if (!ptr) break;
count++;
}
return count;
}
int main() {
char * sentence = "This is,a function... to||count words";
int count = countWords(sentence);
printf("%d\n", count); //====> 7
}
EDIT : Reusing the same functions here is another example that allocates substrings dynamically :
int main() {
char * sentence = "This is,a function... to||split words";
int count = countWords(sentence);
char * ptr = sentence, *start, *end;
char ** substrings = malloc(count * sizeof(char *));
int i=0;
while((ptr = jumpSeparator(ptr)) && ptr[0]) {
start = ptr;
ptr = findEndOfWord(ptr);
end = ptr;
int len = end-start;
char * newString = malloc(len + 1);
memcpy(newString, start, len);
newString[len] = 0;
substrings[i++] = newString;
}
// Prints the result
for(int i=0; i<count; i++) printf("%s\n", substrings[i]);
// Frees the allocated memory
for(int i=0; i<count; i++) free(substrings[i]);
free(substrings);
return 0;
}
Output :
This
is
a
function
to
split
words
I am in the stage of preparing myself for exams, and the thing that I m least proud of are my skills with strings. What I need to do is remove a word from a sentence, without using <string.h> library at all.
This is what I've got so far. It keeps showing me that certain variables are not declared, such as start and end.
#include <stdio.h>
/* Side function to count the number of letters of the word we wish to remove */
int count(char *s) {
int counter = 0;
while (*s++) {
counter++;
s--;
return counter;
}
/* Function to remove a word from a sentence */
char *remove_word(const char *s1, const char *s2) {
int counter2 = 0;
/* We must remember where the string started */
const char *toReturn = s1;
/* Trigger for removing the word */
int found = 1;
/* First we need to find the word we wish to remove [Don't want to
use string.h library for anything associated with the task */
while (*s1 != '\0') {
const char *p = s1;
const char *q = s2;
if (*p == *q)
const char *start = p;
while (*p++ == *q++) {
counter2++;
if (*q != '\0' && counter2 < count(s2))
found = 0;
else {
const char *end = q;
}
}
/* Rewriting the end of a sentence to the beginning of the found word */
if (found) {
while (*start++ = *end++)
;
}
s1++;
}
return toReturn;
}
void insert(char niz[], int size) {
char character = getchar();
if (character == '\n')
character = getchar();
int i = 0;
while (i < size - 1 && character != '\n') {
array[i] = character;
i++;
character = getchar();
}
array[i] = '\0';
}
int main() {
char stringFirst[100];
char stringSecond[20];
printf("Type your text here: [NOT MORE THAN 100 CHARACTERS]\n");
insert(stringFirst, 100);
printf("\nInsert the word you wish to remove from your text.");
insert(stringSecond, 20);
printf("\nAfter removing the word, the text looks like this now: %s", stringFirst);
return 0;
}
your code is badly formed, i strongly suggest compiling with:
gcc -ansi -Wall -pedantic -Werror -D_DEBUG -g (or similar)
start with declaring your variables at the beginning of the function block, they are known only inside the block they are declared in.
your count function is buggy, missing a closing '}' (it doesn't compile)
should be something like
size_t Strlen(const char *s)
{
size_t size = 0;
for (; *s != '\n'; ++s, ++size)
{}
return size;
}
implementing memmove is much more efficient then copy char by char
I reformatted you code for small indentation problems and indeed indentation problems indicate real issues:
There is a missing } in count. It should read:
/* Side function to count the number of letters of the word we wish to remove */
int count(char *s) {
int counter = 0;
while (*s++) {
counter++;
}
return counter;
}
or better:
/* Side function to count the number of letters of the word we wish to remove */
int count(const char *s) {
const char *s0 = s;
while (*s++) {
continue;
}
return s - s0;
}
This function counts the number of bytes in the string, an almost exact clone of strlen except for the return type int instead of size_t. Note also that you do not actually use nor need this function.
Your function insert does not handle EOF gracefully and refuses an empty line. Why not read a line with fgets() and strip the newline manually:
char *input(char buf[], size_t size) {
size_t i;
if (!fgets(buf, size, stdin))
return NULL;
for (i = 0; buf[i]; i++) {
if (buf[i] == '\n') {
buf[i] = '\0';
break;
}
}
return buf;
}
In function remove_word, you should define start and end with a larger scope, typically the outer while loop's body. Furthermore s1 should have type char *, not const char *, as the phrase will be modified in place.
You should only increment p and q if the test succeeds and you should check that p and q are not both at the end of their strings.
last but not least: you do not call remove_word in the main function.
The complete code can be simplified into this:
#include <stdio.h>
/* Function to remove a word from a sentence */
char *remove_word(char *s1, const char *s2) {
if (*s2 != '\0') {
char *dst, *src, *p;
const char *q;
dst = src = s1;
while (*src != '\0') {
for (p = src, q = s2; *q != '\0' && *p == *q; p++, q++)
continue;
if (*q == '\0') {
src = p; /* the word was found, skip it */
} else {
*dst++ = *src++; /* otherwise, copy this character */
}
}
*dst = '\0'; /* put the null terminator if the string was shortened */
}
return s1;
}
char *input(char buf[], size_t size) {
size_t i;
if (!fgets(buf, size, stdin))
return NULL;
for (i = 0; buf[i]; i++) {
if (buf[i] == '\n') {
buf[i] = '\0';
break;
}
}
return buf;
}
int main() {
char stringFirst[102];
char stringSecond[22];
printf("Type your text here, up to 100 characters:\n");
if (!input(stringFirst, sizeof stringFirst))
return 1;
printf("\nInsert the word you wish to remove from your text: ");
if (!input(stringSecond, sizeof stringSecond))
return 1;
printf("\nAfter removing the word, the text looks like this now: %s\n",
remove_word(stringFirst, stringSecond));
return 0;
}
Your start and end pointers are defined within a block which makes their scope limited within that block. So, they are not visible to other parts of your code, and if you attempt to reference them outside their scope, the compiler will complain and throw an error. You should declare them at the beginning of the function block.
That said, consider the following approach to delete a word from a string:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int delete_word(char *buf,
const char *word);
int main(void)
{
const char word_to_delete[] = "boy";
fputs("Enter string: ", stdout);
char buf[256];
fgets(buf, sizeof(buf), stdin);
if (delete_word(buf, word_to_delete))
{
printf("Word %s deleted from buf: ", word_to_delete);
puts(buf);
}
else
{
printf("Word %s not found in buf: ", word_to_delete);
puts(buf);
}
system("PAUSE");
return 0;
}
int chDelimit(int ch)
{
return
(ch == '\n' || ch == '\t') ||
(ch >= ' ' && ch <= '/') ||
(ch >= ':' && ch <= '#') ||
(ch >= '[' && ch <= '`') ||
(ch >= '{' && ch <= '~') ||
(ch == '\0');
}
char *find_pattern(char *buf,
const char *pattern)
{
size_t n = 0;
while (*buf)
{
while (buf[n] && pattern[n])
{
if (buf[n] != pattern[n])
{
break;
}
n++;
}
if (!pattern[n])
{
return buf;
}
else if (!*buf)
{
return NULL;
}
n = 0;
buf++;
}
return NULL;
}
char *find_word(char *buf,
const char *word)
{
char *ptr;
size_t wlen;
wlen = strlen(word);
ptr = find_pattern(buf, word);
if (!ptr)
{
return NULL;
}
else if (ptr == buf)
{
if (chDelimit(buf[wlen]))
{
return ptr;
}
}
else
{
if (chDelimit(ptr[-1]) &&
chDelimit(ptr[wlen]))
{
return ptr;
}
}
ptr += wlen;
ptr = find_pattern(ptr, word);
while (ptr)
{
if (chDelimit(ptr[-1]) &&
chDelimit(ptr[wlen]))
{
return ptr;
}
ptr += wlen;
ptr = find_pattern(ptr, word);
}
return NULL;
}
int delete_word(char *buf,
const char *word)
{
size_t n;
size_t wlen;
char *tmp;
char *ptr;
wlen = strlen(word);
ptr = find_word(buf, word);
if (!ptr)
{
return 0;
}
else
{
n = ptr - buf;
tmp = ptr + wlen;
}
ptr = find_word(tmp, word);
while (ptr)
{
while (tmp < ptr)
{
buf[n++] = *tmp++;
}
tmp = ptr + wlen;
ptr = find_word(tmp, word);
}
strcpy(buf + n, tmp);
return 1;
}
If you have to do it manually, just loop over the indicies of your string to find the first one that matches and than you’ll have a second loop that loops for all the others that matches and resets all and jumps to the next index of the first loop if not matched something in order to continue the searching. If I recall accuretaly, all strings in C are accesible just like arrays, you’ll have to figure it out how. Don’t afraid, those principles are easy! C is an easy langugae, thiught very long to write.
In order to remove: store the first part in an array, store the second part in an array, alloc a new space for both of them and concatinate them there.
Thanks, hit the upvote button.
Vitali
EDIT: use \0 to terminate your newly created string.
I need help with a couple of things:
I'm trying to delete a word from a pointer and put it in a new pointer with a new length but i am not able to copy it to the new pointer
I'm not sure when should I use the free() function.
when I use the free(str) in the delete function it crashes.
After I copy the "str" to the "newStr" what is the best way to copy the "newStr" back to the "str" with the new length?
Please help me understand it, I'm new with this and I googled it, I tried looking here and didn't find something that could help me.
void delete(char *str)
{
int i, indexStart = 0, indexEnd = 0, wordlen = 0, newLen = 0, len = 0;
printf("Enter the index of the word that you want to remove: ");
scanf("%d", &i);
indexs(i, str,&indexStart,&indexEnd,&wordlen);
len = strlen(str);
newLen = len - wordlen - 1;
char *newStr = (char*)malloc(newLen * sizeof(char));
if (newStr == NULL)
{
printf("Error! memory not allocated.");
exit(0);
}
for (int j = 0; j < len; j++)
{
if (j< (indexStart - 1) || j > indexEnd)
{
*newStr = *str;
newStr++;
}
str++;
}
free(str);
//free(newStr);
printf("The new string: %s\n", newStr);
}
void main()
{
char *str = (char*)malloc(1 * sizeof(char));
if (str == NULL)
{
printf("Error! memory not allocated.");
exit(0);
}
text(str);
if (str != NULL)
{
delete(str);
}
free(str);
system("pause");
}
According to the structured programming paradigm your functions should solve small separate tasks. But your function delete() prints to the console, scans input, allocates new string and fills this new string. But what's event worse is the call exit() in this function. If something went wrong, function must to return an error, but not to stop the program. Also names of functions should relfect what they do.
Use free() for every memory block allocated by malloc().
So, this is a working code:
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#include <malloc.h>
const char *findWord(const char *str, const char *delimiters, unsigned index) {
// validate input parameters
if (!str || !delimiters) {
return NULL;
}
// count words
unsigned count = 0;
while (*str && count < index) {
// skip delimiters
while (*str && !strchr(delimiters, *str)) {
str++;
}
if (*str) {
count++;
}
// skip word
while (*str && strchr(delimiters, *str)) {
str++;
}
}
// if index is too big returns NULL
return *str ? str : NULL;
}
unsigned countLengthOfWord(const char *str, const char *delimiters) {
// validate input parameters
if (!str || !delimiters) {
return 0;
}
// count length
unsigned length = 0;
while (*str && !strchr(delimiters, *str++)) {
length++;
}
return length;
}
char *cutWord(char *str, const char *delimiters, unsigned index) {
// validate input parameters
if (!str) {
return NULL;
}
str = (char *)findWord(str, delimiters, index);
// if index is too big, return NULL
if (!str) {
return NULL;
}
// allocate new string for word
unsigned length = countLengthOfWord(str, delimiters);
char *word = malloc(length + 1);
// check if allocation was successfull
if (!word) {
return NULL;
}
// copy word
strncpy(word, str, length);
word[length] = '\0';
// cut word from string
const char *ptr = str + length;
while (*ptr) {
*str++ = *ptr++;
}
*str = '\0';
return word;
}
int main() {
char str1[] = "Hello, my world!";
char str2[] = "Hello, my world!";
char str3[] = "Hello, my world!";
char *word1 = cutWord(str1, " ,!", 0);
char *word2 = cutWord(str2, " ,!", 1);
char *word3 = cutWord(str3, " ,!", 2);
if (word1) {
printf("word: %s\nstring: %s\n\n", word1, str1);
}
if (word2) {
printf("word: %s\nstring: %s\n\n", word2, str2);
}
if (word3) {
printf("word: %s\nstring: %s\n\n", word3, str3);
}
// release allocated memory
free(word1);
free(word2);
free(word3);
getchar();
return 0;
}
I am parsing a file in C, line by line. Here is an exemple of what I am trying to do :
I have a line for example :
word word word WORDTOFIND: word1 word2 word word
What I want to do is : When I find the word WORDTOFIND, get the two next words (word1 and word2 in this case) of the line. Is there an easy way to do that in C ? I know about the strstr function, but I don't find a way to get the next two words word1 and word2 after I found the good one.
One approach would be this:
int main(void)
{
char *str = "rated rat cat bat hat";
char *key = "rat ";
char *pointer = NULL;
char nwords = 2;
if ((pointer = strstr(str, key)) != NULL)
{
while (*pointer != ' ') pointer++;
while (nwords >= 0)
{
printf("%c", *pointer);
if (*pointer == ' ') {
nwords--;
} else if (*pointer == '\0') {
exit(0);
}
pointer++;
}
}
}
You can try an aproach like this, using strtok to parse the words at every space. This code also uses malloc and realloc to allocate space for an array of strings, and grows it when needed.
The code looks like this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define MAXCHAR 100
void exit_if_null(void *ptr, const char *msg);
char *stripped_word(char *word);
int
main(int argc, char const *argv[]) {
FILE *filename;
char line[MAXCHAR];
char *word, *newword;
char **allwords;
int init_size = 8, count = 0, i;
const char *key = "WORDTOFIND";
filename = fopen("files.txt", "r");
if (filename == NULL) {
fprintf(stderr, "%s\n", "Error reading file!");
exit(EXIT_FAILURE);
}
allwords = malloc(init_size * sizeof(*allwords));
exit_if_null(allwords, "Initial Allocation");
while (fgets(line, MAXCHAR, filename) != NULL) {
word = strtok(line, " \n");
while (word != NULL) {
if (count == init_size) {
init_size *= 2;
allwords = realloc(allwords, init_size * sizeof(*allwords));
}
allwords[count] = malloc(strlen(word)+1);
exit_if_null(allwords[count], "Initial Allocation");
newword = stripped_word(word);
strcpy(allwords[count], newword);
count++;
word = strtok(NULL, " \n");
free(newword);
}
}
for (i = 0; i < count; i++) {
if (strcmp(key, allwords[i]) == 0) {
printf("Next two words:\n");
printf("%s\n", allwords[i+1]);
printf("%s\n", allwords[i+2]);
}
free(allwords[i]);
allwords[i] = NULL;
}
free(allwords);
allwords = NULL;
return 0;
}
void
exit_if_null(void *ptr, const char *msg) {
if (!ptr) {
printf("Unexpected null pointer: %s\n", msg);
exit(EXIT_FAILURE);
}
}
char
*stripped_word(char *word) {
int i, pos = 0;
char *result;
result = malloc(strlen(word)+1);
exit_if_null(result, "Initial Allocation");
for (i = 0; word[i] != '\0'; i++) {
if (isalpha(word[i]) || isdigit(word[i])) {
result[pos++] = word[i];
}
}
result[pos] = '\0';
return result;
}
I have a structure
typedef struct store
{
char name[11];
int age;
} store;
and a main function(below is part of it):
int main()
{
int i=0;
int inputs;
char line[100];
char name[11];
char command[11];
store read[3000];
while(i < 3000 && gets(line) != NULL)
{
int tempage;
inputs = sscanf(line, "%10s %10s %d", command, name, &tempage);
if (inputs == 3)
{
if (strcmp(command, "register") == 0)
{
strncpy(read[i].name, name,10);
read[i].age = tempage;
i++;
....
I need to modify it so that it can read a line of arbitrary length, and store the name from the line which is also a string of arbitrary length using malloc and realloc.
How should I approach this?
What you need to do is read the line in smaller increments, and resize your buffer as you go.
As an example (not tested and not meaning to be particularly elegant, just an example):
char *readline(FILE *f)
{
char *buf = NULL;
size_t bufsz = 0, len = 0;
int keep_going = 1;
while (keep_going)
{
int c = fgetc(f);
if (c == EOF || c == '\n')
{
c = 0; // we'll add zero terminator
keep_going = 0; // and terminate the loop afterwards
}
if (bufsz == len)
{
// time to resize the buffer.
//
void *newbuf = NULL;
if (!buf)
{
bufsz = 512; // some arbitrary starting size.
newbuf = malloc(bufsz);
}
else
{
bufsz *= 2; // issue - ideally you'd check for overflow here.
newbuf = realloc(buf, bufsz);
}
if (!newbuf)
{
// Allocation failure. Free old buffer (if any) and bail.
//
free(buf);
buf = NULL;
break;
}
buf = newbuf;
}
buf[len++] = c;
}
return buf;
}
Change the name[11] to *name;
Allocate memory for that everytime using malloc.
By the way, register is a keyword in C language. You can't use it like you did !
I think what you're looking for is:
char* name;
name = (char*)malloc(sizeof(char));
This alternative approach is similar to #asveikau's, but economize on the use of malloc() by copying on the stack.
Please do not use this for homework answer.
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
char * slurponeline(FILE *f, int s) {
const int size = 4096;
char buffer[size];
char * r;
int c,i=0;
while( i<size && (c = fgetc(f),c>=0 && c!='\n')) buffer[i++]=c;
if (0 == s && 0 == i) return 0;
r = (size==i)? slurponeline(f,s+size):malloc(s+i);
memcpy(r+s,buffer,i);
return r;
}
int main(int argc, char ** argv) {
FILE * f = fopen(argc>1?argv[1]:"a.out","rb");
char * a,*command,*commandend,*name,*nameend;
int age;
while (a = slurponeline(f,0)) {
char * p = a;
while (*p && *p == ' ') ++p; // skip blanks.
command = p;
while (*p && *p != ' ') ++p; // skip non-blanks.
commandend = p;
while (*p && *p == ' ') ++p; // skip blanks.
name = p;
while (*p && *p != ' ') ++p; // skip non-blanks.
nameend = p;
while (*p && *p == ' ') ++p; // skip blanks.
age = atoi(p);
*commandend=0;
*nameend=0;
printf("command: %s, name: %s, age: %d\n",command,name,age);
free(a);
}
}