Convert encoding of given string from CP1252 to UTF-8 in C using iconv(3).

cp1252_to_utf8.c

/* Public domain */

/* Author: silvioprog */

/*
    Build and test:

    $ gcc cp1252_to_utf8.c
    $ ./a.out 
    A função atou() é incrível!

    Valgrind dump:

    $ valgrind --show-error-list=yes --tool=memcheck --gen-suppressions=all --leak-check=full --leak-resolution=med --track-origins=yes --vgdb=no ./a.out 
    ==22979== Memcheck, a memory error detector
    ==22979== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
    ==22979== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
    ==22979== Command: ./a.out
    ==22979== 
    A função atou() é incrível!
    ==22979== 
    ==22979== HEAP SUMMARY:
    ==22979==     in use at exit: 0 bytes in 0 blocks
    ==22979==   total heap usage: 14 allocs, 14 frees, 35,631 bytes allocated
    ==22979== 
    ==22979== All heap blocks were freed -- no leaks are possible
    ==22979== 
    ==22979== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

    Feel free to use or improve it and have a lot of fun! (:
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <iconv.h>

static char *atou(const char *str) {
    char *res, *out, *tmp;
    size_t len, obl, ibl, diff;
    iconv_t ic;
    len = strlen(str);
    if (len < 1)
        return NULL;
    res = NULL;
    obl = len;
    ibl = len;
    ic = iconv_open("UTF-8", "CP1252");
    if (ic != (iconv_t) -1) {
        res = malloc(len + 1);
        if (!res) {
            iconv_close(ic);
            return NULL;
        }
        out = res;
        while (ibl > 0)
            if (iconv(ic, (char **) &str, &ibl, &out, &obl) == -1) {
                if (errno == E2BIG) {
                    diff = out - res;
                    len += ibl;
                    obl += ibl;
                    tmp = realloc(res, len + 1);
                    if (tmp) {
                        res = tmp;
                        out = res + diff;
                        continue;
                    }
                }
                free(res);
                res = NULL;
                break;
            }
        iconv_close(ic);
    }
    if (res) {
        len -= obl;
        res[len] = 0;
    }
    return res;
}

int main(void) {
    char *str = atou("A fun\xe7\xe3o atou() \xe9 incr\xedvel!");
    printf("%s\n", str);
    free(str);
    return EXIT_SUCCESS;
}