Read a string from stdin and convert it from UTF-8 to an encoding of your choice, and print the byte values

byteecho.c

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


void print_bytes(const char* prefix, const char* str, size_t len);


int main(int argc, char* argv[]) {
    if (argc != 2) {
        fputs("Usage: ./byteecho <encoding>\n", stderr);
        return 1;
    }
    char* buffer = NULL;
    ssize_t len; 
    size_t capacity = 0;
    iconv_t cd = iconv_open(argv[1], "UTF-8");
    if (cd == (iconv_t) -1) {
        if (errno == ENFILE) {
            fputs("Error: too many files are open.\n", stderr);
        } else if (errno == EINVAL) {
            fprintf(stderr, "Error: converting to %s is not supported.\n", argv[1]);
        } else if (errno == ENOMEM) {
            fputs("Program error (out of memory)\n", stderr);
        } else if (errno == EMFILE) {
            fputs("Program error (process has max file descriptors open)\n", stderr);
        } else {
            fputs("Program error (unknown)", stderr);
        }
        return 2;
    }
    while ((len = getline(&buffer, &capacity, stdin)) != -1) {
        /* Truncate the trailing newline. */
        buffer[--len] = '\0';
        /* A lot of extra space for bigger encoding. */
        size_t len_koi = len*5 + 3;
        char* buffer_in_koi = malloc(len_koi);
        /* Make copies for iconv. */
        char* buffer_end = buffer, *buffer_in_koi_end = buffer_in_koi;
        size_t bytes_left = len, bytes_left_koi = len_koi;
        size_t err = iconv(cd, &buffer_end, &bytes_left, &buffer_in_koi_end, &bytes_left_koi);
        if (err == (size_t) -1) {
            if (errno == EILSEQ) {
                fputs("Error: invalid byte sequence in the input.\n", stderr);
            } else if (errno == EINVAL) {
                fputs("Error: incomplete byte sequence at end of input.\n", stderr);
            } else if (errno == E2BIG) {
                fputs("Program error (output buffer too small)\n", stderr);
            } else if (errno == EBADF) {
                fputs("Program error (invalid iconv_t handle)\n", stderr);
            } else {
                fputs("Program error (unknown)\n", stderr);
            }
            continue;
        }
        print_bytes("UTF-8", buffer, len);
        print_bytes(argv[1], buffer_in_koi, len_koi - bytes_left_koi);
    }
    iconv_close(cd);
    return 0;
}


void print_bytes(const char* encoding, const char* str, size_t len) {
    unsigned int width_so_far = 3;
    printf("In %s:\n   ", encoding);
    for (size_t i = 0; i < len; i++) {
        if (width_so_far > 75) {
            printf("\n   ");
            width_so_far = 3;
        }
        printf("%.2x ", (unsigned char)str[i]);
        width_so_far += 3;
    }
    printf("\n");
}