vsscanf(3) - sscanf(3) with a va_list parameter


#include <slack/std.h>
#include <slack/vsscanf.h>

int vsscanf(const char *str, const char *format, va_list args);


Similar to sscanf(3) with the variable argument list specified directly as for vprintf(3).

Note that this may not be identical in behaviour to the sscanf(3) on your system because this was implemented from scratch for systems that lack vsscanf(3). So your sscanf(3) and this vsscanf(3) share no common code. Your sscanf(3) may support extensions that vsscanf(3) does not support. vsscanf(3) complies with all of the relevant ISO C requirements for sscanf(3) except:


MT-Safe if and only if no thread calls setlocale(3). Since locales are inherently non-threadsafe as they are currently defined, this shouldn't be a problem. Just call setlocale(LC_ALL, "") once after program initialisation and never again (at least not after creating any threads). If it is a problem, just change localeconv()->decimal_point[0] in the source to '.', and it will be MT-Safe at the expense of losing locale support.


#include <slack/std.h>
#include <slack/vsscanf.h>

int fdscanf(int fd, const char *format, ...)
    va_list args;
    char buf[BUFSIZ];
    ssize_t bytes;
    int rc;
    if ((bytes = read(fd, buf, BUFSIZ)) <= 0)
        return bytes;

    buf[bytes] = '\0';

    va_start(args, format);
    rc = vsscanf(buf, format, args);

    return rc;

int main()
    int rc, a = 0, b = 0;

    rc = fdscanf(STDIN_FILENO, "%d %d", &a, &b);
    printf("rc = %d a = %d b = %d\n", rc, a, b);

    return (rc == 2) ? EXIT_SUCCESS : EXIT_FAILURE;


gcc(1) warns that:

warning: ANSI C does not support the `L' length modifier
warning: use of `l' length character with `e' type character

However, the ANSI C standard (Section states that:

"Finally, the conversion specifiers e, f, and g shall be preceded by l if the corresponding argument is a pointer to double rather than a pointer to float, or by L if it is a pointer to long double."

I have chosen to disregard the gcc(1) warnings in favour of the standard. If you see the above warnings when compiling the unit tests for vsscanf(3), just ignore them.


libslack(3), sscanf(3)


20230824 raf <>