Technical Q&A QA1549

Expanding Tilde-based paths

Q: How do I expand a tilde-based path to its full path value?

A: How do I expand a tilde-based path to its full path value?

Some situations may arise where you would like to expand a tilde-based relevant path into a resolved, absolute path. For example "~/" might resolve to "/Users/johndoe". Here are examples on how to accomplish this task under each development environment (Objective-C, POSIX and Core Foundation).

Listing 1 Objective-C (result is autoreleased)

NSString *result = [@"~/Desktop" stringByExpandingTildeInPath];

Listing 2 POSIX (caller responsible for freeing result)

#include <glob.h>

char* CreatePathByExpandingTildePath(char* path)
{
    glob_t globbuf;
    char **v;
    char *expandedPath = NULL, *result = NULL;

    assert(path != NULL);

    if (glob(path, GLOB_TILDE, NULL, &globbuf) == 0) //success
    {
        v = globbuf.gl_pathv; //list of matched pathnames
        expandedPath = v[0]; //number of matched pathnames, gl_pathc == 1

        result = (char*)calloc(1, strlen(expandedPath) + 1); //the extra char is for the null-termination
        if(result)
            strncpy(result, expandedPath, strlen(expandedPath) + 1); //copy the null-termination as well

        globfree(&globbuf);
    }

    return result;
}

Listing 3 Core Foundation (caller responsible for releasing result)

#include <glob.h>

// This is the POSIX version in listing 2.
char*  CreatePathByExpandingTildePath(char* path);

CFStringRef CreateCFStringByExpandingTildePath(CFStringRef path)
{
    char pcPath[PATH_MAX];
    char *pcResult = NULL;
    CFStringRef result = NULL;

    if (CFStringGetFileSystemRepresentation(path, pcPath, PATH_MAX)) //CFString to CString
    {
        pcResult = CreatePathByExpandingTildePath(pcPath); //call the POSIX version
        if (pcResult)
        {
            result = CFStringCreateWithCString(NULL, pcResult, kCFStringEncodingUTF8); //CString to CFString
            free(pcResult); //free the memory allocated in CreatePathByExpandingTildePath()
        }
    }

    return result;
}

Document Revision History

Date	Notes
2008-09-08	Simplified POSIX and CF versions using the embedded glob() function.
2007-09-24	New document that demonstrates how to resolve tilde-based relevant paths.