Is there any replacements for strstr in C/C++ that can be used with multibyte strings?

Question

I am trying to do strstr in C++ with Shift-JIS strings. But since the accepted answer here states that there could be false positives if the standard strstr is used, I couldn't just use the regular one in the standard library. Apparently Windows provides _mbsstr that does what I want, but I am targeting other platforms as well.

I tried to use gnulib as it also provides mbsstr but I couldn't get it to work as it requires autotools, and I am using cmake.

Is there anything else that achieves it?

Answer 1

You are correct: unlike UTF-8, the Shift-JIS encoding causes false positives for strstr and strchr for single byte characters.

Here is a simplistic custom function for C:

#include <string.h>

char *sjis_strstr(const char *s1, const char *s2) {
    unsigned char c1, c2 = *s2++;
    if (c2 == '\0')
        return s1;
    size_t len2 = strlen(s2);
    while ((c1 = *s1++) != '\0') {
        if (c1 == c2 && !strncmp(s1, s2, len2))
            return (char *)(s1 - 1);
        if (*s1 == '\0')
            break;
        s1 += (c1 >= 0x81 && c1 <= 0x9F) || (c1 >= 0xE0 && c1 <= 0xFC);
    }
    return NULL;
}