27.10 Parse State, Restartable Functions: variable name

[happysalada]

I have to say i'm a little confused by then naming of variable in that example

// mbsrtowcs() modifies the input pointer to point at the first
    // invalid character, or NULL if successful. Let's make a copy of
    // the pointer for mbsrtowcs() to mess with so our original is
    // unchanged.
    const char *invalid = mb_string;

Why call it invalid in this case?
I initially thought you wanted to show a case where the conversion is failing. Instead it's a case where the conversion succeeds.
I personally think that the invalid case would be interesting.
If you keep the valid case, how about showing a multi-threaded example? (I understand you might not want to digress too much).
Otherwise, how about renaming the variable maybe_invalid or even maybe_invalid_but_valid_here
(I understand C likes to name variable with way too few characters, so feel free to reject those on those grounds)

[beejjorgensen]

I've modded the example to show handling of success and failure (although the example will still probably succeed on all platforms). Cheers!

#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <wchar.h>
#include <string.h>
#include <locale.h>

int main(void)
{
    // Get out of the C locale to one that likely has the euro symbol
    setlocale(LC_ALL, "");

    // Original multibyte string with a euro symbol (Unicode point 20ac)
    char *mb_string = "The cost is \u20ac1.23";  // €1.23
    size_t mb_len = strlen(mb_string);

    // Wide character array that will hold the converted string
    wchar_t wc_string[128];  // Holds up to 128 wide characters

    // Set up the conversion state
    mbstate_t mbs;
    memset(&mbs, 0, sizeof mbs);  // Initial state

    // mbsrtowcs() modifies the input pointer to point at the first
    // invalid character, or NULL if successful. Let's make a copy of
    // the pointer for mbsrtowcs() to mess with so our original is
    // unchanged.
    //
    // This example will probably be successful, but we check farther
    // down to see.
    const char *invalid = mb_string;

    // Convert the MB string to WC; this returns the number of wide chars
    size_t wc_len = mbsrtowcs(wc_string, &invalid, 128, &mbs);

    if (invalid == NULL) {
        printf("No invalid characters found\n");

        // Print result--note the %ls for wide char strings
        printf("multibyte: \"%s\" (%zu bytes)\n", mb_string, mb_len);
        printf("wide char: \"%ls\" (%zu characters)\n", wc_string, wc_len);
    } else {
        ptrdiff_t offset = invalid - mb_string;
        printf("Invalid character at offset %td\n", offset);
    }
}