检查输入字符串是否为ASCII码

今天从Wireshark代码里面看见一段用于检查字符是否为ASCII字符的代码，写的很好，很有创意，贴在这里。由于Wireshark遵循GPL，所以如果万一有人恰好需要这种功能的代码并从这里摘取了代码的话，请遵循GPL协议。

/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.

 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#include <stdio.h>
#include <string.h>

/* chars allowed in field abbrev */
static const char fld_abbrev_chars[256] = {
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x00-0x0F */
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x10-0x1F */
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, /* 0x20-0x2F '-', '.' */
 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, /* 0x30-0x3F '0'-'9' */
 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, /* 0x40-0x4F 'A'-'O' */
 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, /* 0x50-0x5F 'P'-'Z', '_' */
 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, /* 0x60-0x6F 'a'-'o' */
 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, /* 0x70-0x7F 'p'-'z' */
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x80-0x8F */
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x90-0x9F */
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0xA0-0xAF */
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0xB0-0xBF */
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0xC0-0xCF */
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0xD0-0xDF */
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0xE0-0xEF */
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0xF0-0xFF */
};

char check_charset(const char table[256], const char *str)
{
    const char *p = str;
    char c;

    do {
      c = *(p++);
      printf("Checking: %c, result: %d\n", c, table[c]);
    } while (table[c]);
    return c;
}

int main(int argc, char *argv[])
{
    char input[256]={'\0'};
    int lenght, ret;
    char c;

    if (argc == 1){
        printf ("Usage %s STRING.\n", argv[0]);
        return -1;
    }

    if (strncpy(input, argv[1], 255) == NULL){
        perror("Failed to copy inputed string.\n");
        return -1;
    }

    c = check_charset(fld_abbrev_chars, input);
    if (c){
        printf ("Invalid char: %c\n", c);
        return -1;
    }
    else
        printf ("Good string: %s\n", input);
    return 0;
}