C buffer overflow
buffer-overflow, c, char, string
Solution
It looks like you've got your `strncpy` arguments mixed up: the second argument is the source string, not the limit on the number of chars to copy, which should be the third argument:
strncpy(x, p, r - p); // copy r - p chars from p to x
Furthermore, you want to use `strcat` instead of `strcpy`. Using `strcpy`, you'll just overwrite the contents of the result with the replacement string, every time. Using `strcat`, be sure to initialize the result with `\0` before starting.
Finally, you're returning a reference to a local variable `x` from your function: you can't do this as the memory isn't usable after the function returns.
Problem
I tried to make a function that replaces all occurrences of `str1` in a text `t` with `str2` but I keep getting a "buffer overflow" error message. Can you please tell me what is wrong with my function? ``` #include <stdio.h> #include <string.h> #include <assert.h> //replace all *str1 in *t with *str2, put the result in *x, return *x char * result(char *str1,char *str2,char *t) { char *x=NULL,*p=t,*r=t; x=malloc(400*sizeof(char)); assert(x!=NULL); x[0]='\0'; r=strstr(t,str1); //r is at the first occurrence of str1 in t, p is at the beginning of t while(r!=NULL) { strncat(x,p,r-p); //copy r-p chars from p to x strcat(x,str2); //copy str2 to x p=r+strlen(str1); //p will be at the first char after the last occurrence of str1 in t r=strstr(r+strlen(str1),str1); //r goes to the next occurrence of str1 in t } strcat(x,p); return x; } ``` I did not used the `gets()` function to read any `char` array. My compiler is gcc version 4.6.3 I updated the code, it works, but the result is not the as expected. `main()` function: ``` int main(void) { char *sir="ab",*sir2="xyz",*text="cabwnab4jkab",*final; final=result(sir,sir2,text); puts(final); free(final); return 0; } ``` printed string: ``` b ``` I expected `cxyzwnxyz4jkxyz`