Struggling with strcat function in C

Question

I am really frusted with my program right now. I expect that the strcat function would simply concatenate the desired strings together but apparently the strcat function (when uncommented) doesn't get the concatenation correct, and somehow changes the value of my variables. As is, the correct result if printed, for example:

/usr/local/sbin
/usr/local/sbin
/usr/local/bin
/usr/local/bin
/usr/sbin
/usr/sbin
... (etc)

But when these two lines are uncommented

//strcat(file_loc, slash);
//strcat(file_loc, temp);

then here is the bizzare result I get:

/usr/local/sbin
/usr/local/sbin/ls
ls
ls/ls
/usr/sbin
/usr/sbin/ls
... (etc)

Here is the function that I am working on. Help would be very much appreciated.

void step_four (void) {
    int n=0;
    int has_slash=0;
    const char * slash="/";
    char * aa;
    char bb[64];
    int cc=0;
    int len;
    char * file_loc = malloc(100);
    char * temp= malloc(100);
    char * temp2 = malloc(100);
    //char [] f="FOO";


    printf("XXXXXXXXXXXXXXXXXXXXXXXX\n");
    printf("Made it to step 4\n");
    printf("First word of command is: %s\n", words[0]);

    aa = words[0];
    len = strlen(aa);

    while (cc < len) {
        bb[cc] = *(aa + cc);
        cc++;
    }

    while(n < len) {
        if (bb[n++] == '/') {
            //printf("HELLO !!\n");
            has_slash=1;
            break;
        }
    }


    //printf("has_slash=%d\n", has_slash);

    n=0;

    while (paths[n] != NULL) {
        //printf("%s\n", paths[n]);
        file_loc = paths[n];
        //file_loc[strlen(file_loc)]='\0';
        temp = words[0];
        if (has_slash) {
            //do stuff for slash

        }
        else {  
            printf("%s\n", file_loc);
            //strcat(temp2, "a");
            //strcat(file_loc, slash);
            //strcat(file_loc, temp);
            //file_loc[strlen(file_loc)]='/';
            //file_loc[strlen(file_loc) + 1]='/0';
            printf("%s\n", file_loc);
        //  f = file_loc;

        }
        n++;
    }

}

Did you consider using `snprintf` (or `asprintf`) instead of your calls to `strcat`? It probably is better suited for your task, and is much safer! Or, if coding in C++, use `std::string` — Basile Starynkevitch, Feb 02 '13 at 05:48
@StevenC. Where's the rest of your program? @ First question here, please read what to do [when you get answers](http://stackoverflow.com/faq#howtoask). — जलजनक, Feb 02 '13 at 06:03

score 0 · Answer 1 · answered Feb 02 '13 at 05:54

http://www.cplusplus.com/reference/cstring/strcat/

char * strcat ( char * destination, const char * source );

"Appends a copy of the source string to the destination string. The terminating null character in destination is overwritten by the first character of source, and a null-character is included at the end of the new string formed by the concatenation of both in destination."

The above quote is from cplusplus.

Struggling with strcat function in C

1 Answers1