Bdtjtk

I need strtol to convert some numbers from a range of [0 to 255]
how can I check the conversion of 0 if 0 is also a number that i need to convert?

long conv = strtol(argv, &p, 10);

if (conv == 0)

{

    perror("Conversion error");

    exit(EXIT_FAILURE);

}

if ((conv >= LONG_MAX || conv <= LONG_MIN) && errno == 34);

{

    perror("Invalid Range!");

    exit(EXIT_FAILURE);

}

Prior to calling strtol, set errno to 0.

Then after the call, check the value of errno. If it's 0, you know the call was successful. Addtionally, you'll want to check if *p is 0. If so, that means the entire string was parsed successfully with no extra characters.

errno = 0;

long conv = strtol(argv, &p, 10);  

if (errno)

{

    perror("Conversion error");

    exit(EXIT_FAILURE);

}

else if (*p)

{

    perror("Not all characters converted");

    exit(EXIT_FAILURE);

}

The man page also mentions this in the "Notes" section:

Since strtol() can legitimately return 0, LONG_MAX, or LONG_MIN
(LLONG_MAX or LLONG_MIN for strtoll()) on both success and failure,
the calling
program should set errno to 0 before the call, and then determine if an error occurred by checking whether errno has a nonzero
value after the
call.