Question

g++ would nt even compile it. Where was I wrong? These are the error message:

gcc sign.c
sign.c: In function âmainâ:
sign.c:35:2: warning: format not a string literal and no format arguments [-Wformat- security]

==================================================================================

#include "stdio.h"

int string_length(char str[]);
void string_sort(char s[]);

void string_sort(char s[])
{
    char tmpt;
    int i, j, len;
    len=string_length(s);
    for(i=0; i<len-1; i++){
            for (j=i+1; j<len; j++){
                    if (s[i] > s[j]){
                            tmpt=s[i];
                            s[i]=s[j];
                            s[j]=tmpt;
                    }
            }
    }
}


int string_length(char str[]){
    int i;
    for(i=0; i<80; i++){
            if(str[i]=='\0'){
                    return(i);
            }
    }
}

int main(){
    char words[80];
scanf("%s", words);
    printf(words);
    string_sort(words);
    printf(" ");
    printf(words);
    printf("\n");




    while ( words != " "){
            scanf("%s", words);
            printf(words);
            string_sort(words);
            printf(" ");
            printf(words);
            printf("\n");
    }
}

Answer 1

First, that’s just a warning message, which means the compiler detected something probably wrong but compiled your code anyway. Not all compilers give the same warnings, as you’ve noticed.

The problem is this line (and all the other lines like it):

printf(words);

When using printf, you must use a format string, something like this:

printf("%s", words);

Otherwise, if the things you’re printing (words) happens to have any % characters in it, then printf() will treat those as formatting specifiers and try to read arguments that you haven’t supplied.

If you just want to print a string by itself, then puts can be useful:

puts(words);

This prints words followed by a newline.