C: problem with char*

Question

/*
 * code.c
 *
 * TASK
 *      Reverse a string by reversing pointers. Function should use return
 *      type char* and use a char* parameter as input.
 */
#include &l         


        

Answer 1

The parameters does not match up with the variable names.

• sPhrase is declared as an array of chars.
• The function reverse has a parameter sPhrase which is a pointer to an array of chars

This explains why there is a 'type mismatch'. I have included a fixed version, try that.

char* reverse(char *sPhrase);

int main() {
    char sPhrase[STRMAX];
    char sReverse[STRMAX];
    printf("Enter string (max. 50 chars): ");
    gets(sPhrase);
    sReverse = reverse(sPhrase);

    return 0;
}

char* reverse(char* sPhrase) {
    /* char* sOutput[STRMAX];*/
    static char sOutput[STRMAX];
    int iCnt = 0, iCntRev;

    for (iCntRev = strlen(sPhrase)-2; iCntRev >= 0; iCntRev--) {
        sPhrase[iCnt] = sOutput[iCntRev];
        iCnt++;
    }

    sPhrase[iCnt] = '\0';      // Don't forget to close the string

    return sOutput;
}

The compiler is pretty smart to check for 'incompatible' types. C is strict very relaxed when it comes to this kind of thing, so the onus is on you on making sure the declarations match up with the definitions in order for a successful compile.

I have also corrected the problem with using the sOutput variable within the reverse function, and changed it to a static as the variable will go out of scope and will end up with garbage, by prefixing the keyword static will ensure that the variable remains in scope.

Edit: For some reason, I added the strike tag to strike out the line but others are seeing it somehow...???

On closer inspection, the code does not work, I have fixed it, taking into account of other people's inputs and consideration, note I have used fgets instead of the evil gets function as that is a breeding ground for buffer overflows, also changed the function signature to use the const keyword for the parameter.

char * reverse(const char *sPhrase);

int main() {
    char sPhrase[STRMAX];
    char *sReverse;
    printf("Enter string (max. 50 chars): ");
    fgets(sPhrase, STRMAX - 1, stdin);
    sReverse = reverse(sPhrase);
    printf("Reversed string: %s\n", sReverse);
    return 0;
}

char *reverse(const char* sPhrase) {
    char* sOutput;
    int iCnt = 0, iCntRev;
    sOutput = (char *)malloc((STRMAX * sizeof(char)) + 1);
    if (sOutput){
        for (iCntRev = strlen(sPhrase) - 1; iCntRev >= 0; iCntRev--) {
            *sOutput++ = sPhrase[iCntRev];
            iCnt++;
        }
        *sOutput++ = '\0';
    }
    return (sOutput - iCnt);
}

Here's an excellent tutorial on pointers.

Hope this helps, Best regards, Tom.