Segmentation Fault:11 in C [closed] - c

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I am writing a program in C that replaces a number in a char* called "template" with a string, but I continually get a Segmentation Fault: 11 error.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
char *rep_str(const char *s, const char *old, const char *new1){
char *ret;
int i, count = 0;
int newlen = strlen(new1);
int oldlen = strlen(old);
for (i = 0; s[i] != '\0'; i++){
if (strstr(&s[i], old) == &s[i]){
count++;
i += oldlen - 1;
}
}
ret = (char*)malloc(i + count * (newlen - oldlen));
if (ret == NULL)
exit(EXIT_FAILURE);
i = 0;
while (*s){
if (strstr(s, old) == s){ //compare the substring with the newstring
strcpy(&ret[i], new1);
i += newlen; //adding newlength to the new string
s += oldlen;//adding the same old length the old string
} else {
ret[i++] = *s++;
}
}
ret[i] = '\0';
return ret;
}
char* madlib_by_numbers(char* temp, int word_count, char* words[]){
char* numbers[] = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9"};
int tempSize = strlen(temp);
for (int i = 0; i < tempSize; i++){
if (isdigit(temp[i])){
for (int j = 0; j < (sizeof(numbers) / sizeof(char*)); j++){
temp = rep_str(temp, numbers[j], words[j]); //it makes it to this line, but never gets to assert()
}
}
}
return temp;
}
int main() {
char* temp1 = "The 1 0 likes to 2 in the moonlight.";
char* words[] = {"git", "brilliant", "swim"};
char* result = "The brilliant git likes to swim in the moonlight.";
int stringLength = strlen(result);
char* test = madlib_by_numbers(temp1, 3, words);
assert(strncmp(test, result, stringLength) == 0);
free(test);
return 0;
}
and when I run the debugger, it simply says: Segmentation Fault: 11
What i just want to understand is where the segmentation fault error is coming from, I have the suspicion one of my loops is running too many times.

Answer 1

There are a few issue with your code. However, the direct answer to your question is in this loop:
for (int j = 0; j < (sizeof(numbers) / sizeof(char*)); j++){
temp = rep_str(temp, numbers[j], words[j]);
}
You are calling rep_str for every digit while you mean call rep_str only if the digit in temp matches the corresponding digit in numbers. So add this conditional if(strcmp(temp,numbers[j]) == 0) right before the line temp=.... Then it'll solve your current problem.
The segfault is caused because there are only three elements in the words array. Your old loop indexes from 0 to 9 and fails when j=3, out of bound.
Also, delete the free() at the end of your program. test was never allocated and will cause a core dump.

Answer 2

ret = (char*)malloc(i + count * (newlen - oldlen));
There are a few problems with this line of code.
For a start, don't cast malloc (or any void * that you're assigning to a variable of different pointer type, or vice versa).
If you intended to allocate space to store a string, where's the string-terminating '\0' going to go? You need to realise that for an empty old string, this will be malloc(0) and zero bytes is not enough to store an empty string.
There's also a problem if you expect that old may be a substring of new (for example, you're replacing "0" with "hell0"). You'll need to tweak your algorithm to handle this problem. I'll leave that as a challenge for you to attempt :)
for (int i = 0; i < tempSize; i++){
if (isdigit(temp[i])){
for (int j = 0; j < (sizeof(numbers) / sizeof(char*)); j++){
temp = rep_str(temp, numbers[j], words[j]); //it makes it to this line, but never gets to assert()
}
}
}
users previous answer highlighted this code correctly, but not for the right reason... and so the solution he/she presented is wrong.
isdigit(temp[i]) may also cause segfaults for some inputs. I recommend using isdigit((unsigned char) temp[i]) instead, in this case.
It's not valid to access words[j] where word_count is 3 and j is greater or equal to 3; you're accessing that array out of bounds.
You also need to be careful to free any memory you *alloc (while simultaneously not freeing memory that you don't *alloc). Forgetting to do the former won't cause crashes, but your program won't run happily; it'll use heaps of memory.
Consider something like this, instead:
temp = strdup(temp);
if (temp == NULL) {
exit(EXIT_FAILURE);
}
for (int i = 0; i < tempSize; i++){
if (isdigit((unsigned char) temp[i])){
for (int i = min(word_count, sizeof(numbers) / sizeof(char*)), j = 0; j < i; j++){
char *new = rep_str(temp, numbers[j], words[j]);
free(temp);
temp = new;
}
}
}