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cc-stringsansi-c

? operator in sscanf regular expression

I'm trying to parse an extension out of a list of files of the format 'filename.extension'. However in the cases where filename is blank, I'm getting undesired results.

For example....

sscanf(my_string,"%*[^.].%s",file_ext);

Will properly parse the below

foo.gif such that file_ext = gif 
bar.jpg such that file_ext = jpg

However it will fail to parse cases where the prefixed filename is missing. i.e.

.pdf will result in file_ext = NULL

I've tried to use the ? operator after ] to indicate the string may or may not exist; however it's clearly not supported in C. Is there another solution or something I'm overlooking? Thanks!

Solution

  • You can use the standard string function strchr to determine whether a point is present and then use strcpy to copy the file extension. For example

    char *p = strchr( my_string, '.' );
if ( p != NULL ) strcpy( file_ext, p + 1 );

    Or you can use strrchr that finds the last occurrence of a character.

    char *p = strrchr( my_string, '.' );
if ( p != NULL ) strcpy( file_ext, p + 1 );