Getting absolute path of a file

Question

How can I convert a relative path to an absolute path in C on Unix? Is there a convenient system function for this?

On Windows there is a GetFullPathName function that does the job, but I didn't find something similar on Unix...

Answer 1

Use realpath().

The realpath() function shall derive, from the pathname pointed to by file_name, an absolute pathname that names the same file, whose resolution does not involve '.', '..', or symbolic links. The generated pathname shall be stored as a null-terminated string, up to a maximum of {PATH_MAX} bytes, in the buffer pointed to by resolved_name.

If resolved_name is a null pointer, the behavior of realpath() is implementation-defined.

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The following example generates an absolute pathname for the file identified by the symlinkpath argument. The generated pathname is stored in the actualpath array.

#include <stdlib.h> ... char *symlinkpath = "/tmp/symlink/file"; char actualpath [PATH_MAX+1]; char *ptr;   ptr = realpath(symlinkpath, actualpath); 

Answer 2

Try realpath() in stdlib.h

char filename[] = "../../../../data/000000.jpg"; char* path = realpath(filename, NULL); if(path == NULL){     printf("cannot find file with name[%s]\n", filename); } else{     printf("path[%s]\n", path);     free(path); }