how to remove extension from file name?

Question

I want to throw the last three character from file name and get the rest?

I have this code:

char* remove(char* mystr) {

    char tmp[] = {0};
    unsigned int x;

    for (x = 0; x < (strlen(mystr) - 3); x++)
        tmp[x] = mystr[x];

    return tmp;
}

Answer 1

Try:

char *remove(char* myStr) {
    char *retStr;
    char *lastExt;
    if (myStr == NULL) return NULL;
    if ((retStr = malloc (strlen (myStr) + 1)) == NULL) return NULL;
    strcpy (retStr, myStr);
    lastExt = strrchr (retStr, '.');
    if (lastExt != NULL)
        *lastExt = '\0';
    return retStr;
}

You'll have to free the returned string yourself. It simply finds the last . in the string and replaces it with a null terminator character. It will handle errors (passing NULL or running out of memory) by returning NULL.

It won't work with things like /this.path/is_bad since it will find the . in the non-file portion but you could handle this by also doing a strrchr of /, or whatever your path separator is, and ensuring it's position is NULL or before the . position.

---

A more general purpose solution to this problem could be:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// remove_ext: removes the "extension" from a file spec.
//   myStr is the string to process.
//   extSep is the extension separator.
//   pathSep is the path separator (0 means to ignore).
// Returns an allocated string identical to the original but
//   with the extension removed. It must be freed when you're
//   finished with it.
// If you pass in NULL or the new string can't be allocated,
//   it returns NULL.

char *remove_ext (char* myStr, char extSep, char pathSep) {
    char *retStr, *lastExt, *lastPath;

    // Error checks and allocate string.

    if (myStr == NULL) return NULL;
    if ((retStr = malloc (strlen (myStr) + 1)) == NULL) return NULL;

    // Make a copy and find the relevant characters.

    strcpy (retStr, myStr);
    lastExt = strrchr (retStr, extSep);
    lastPath = (pathSep == 0) ? NULL : strrchr (retStr, pathSep);

    // If it has an extension separator.

    if (lastExt != NULL) {
        // and it's to the right of the path separator.

        if (lastPath != NULL) {
            if (lastPath < lastExt) {
                // then remove it.

                *lastExt = '\0';
            }
        } else {
            // Has extension separator with no path separator.

            *lastExt = '\0';
        }
    }

    // Return the modified string.

    return retStr;
}

int main (int c, char *v[]) {
    char *s;
    printf ("[%s]\n", (s = remove_ext ("hello", '.', '/'))); free (s);
    printf ("[%s]\n", (s = remove_ext ("hello.", '.', '/'))); free (s);
    printf ("[%s]\n", (s = remove_ext ("hello.txt", '.', '/'))); free (s);
    printf ("[%s]\n", (s = remove_ext ("hello.txt.txt", '.', '/'))); free (s);
    printf ("[%s]\n", (s = remove_ext ("/no.dot/in_path", '.', '/'))); free (s);
    printf ("[%s]\n", (s = remove_ext ("/has.dot/in.path", '.', '/'))); free (s);
    printf ("[%s]\n", (s = remove_ext ("/no.dot/in_path", '.', 0))); free (s);

    return 0;
}

and this produces:

[hello]
[hello]
[hello]
[hello.txt]
[/no.dot/in_path]
[/has.dot/in]
[/no]