I'm trying to copy a string of characters in another string using dynamic memory allocation but it doesn't work:

#include <stdlib.h>
#include <stdio.h>
int main() {
    char* s1, * s2, * s3;
    s1 = (char*)malloc(11 * sizeof(char));
    s2 = (char*)malloc(11 * sizeof(char));
    s3 = (char*)malloc(11 * sizeof(char));
    fgets(s1, 11, stdin);
    fgets(s2, 11, stdin);
    int i = 0;
    do {
        *(s3   i) = *(s1   i);
        i  ;
    } while (*(s1   i) != '\n' && *(s1   i) != '\0');
    puts(s3);
    return 0;
}

CodePudding user response：

You do not null terminate the s3 string.

    } while (*(s1   i) != '\n' && *(s1   i) != '\0');
    s3[i] = 0;
    puts(s3);

CodePudding user response：

You have a bug here: } while (*(s1 i) != '\n' && *(s1 i) != '\0');.

This means that you stop copying at \n which fgets will place in the buffer but you do not null terminate the string s3.

So if s1 looks like "hello\n\0" then s3 will end up as "hello\n" without null terminator.

Corrected and de-obfuscated loop:

size_t i;
for(i=0; s1[i]!='\n' && s1[i]!='\0'; i  )
{
  s3[i] = s1[i];
}
s3[i] = '\0';