c - C 中的 ispunct() 有异常(exception)吗？

Question

我想编写一个代码来检查 MAC 地址的正确性。输入应类似于 D7:6E:F4:30:17:2B。我正在考虑使用函数 isdigit() 和 isupper()。不知道如何让用户可以写入“:”符号并阻止他写入其他符号。

if(user input is 13:4F:60:AC:7O:DE)
    ... all good
if(user input is 14:a]:!o:0L)
    ... wrong input, retry

编辑据@Woodrow Barlow回答我已经写了该代码:

int mac_address() 
    {   
        int is_valid = 1;
        printf("MAC ADDRESS:");
        fgets(mac_addr, sizeof(mac_addr), stdin); 
            if (mac_addr[sizeof(mac_addr) - 1] != '\0')
            {
                is_valid = 0;
            }
            else if (ether_aton(mac_addr) == NULL)
            {
                is_valid = 0;
                // input isn't recognizable as a MAC address
            }
            if (is_valid == 1)
            {
                system("clear");
                printf("valid!\n");
                printf("%s\n", mac_addr);
                return license_menu();
            }
            else {
                printf("invalid!\n");
                fflush(stdin);
                return 1;
            }
    }

Answer 1

解析 MAC 地址或检查其有效性的最佳方法是使用 ether_aton . MAC 地址可以有多种格式，并且可以依靠 ether_aton 来解析它们。

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <netinet/ether.h>

int main(int argc, const char *argv[])
{
    char mac_addr[64];

    while (true)
    {
        fgets(mac_addr, sizeof(mac_addr), stdin);
        if (mac_addr[sizeof(mac_addr) - 1] != '\0')
        {
            // input was too long for the buffer
            printf("invalid!\n");
        }
        else if (ether_aton(mac_addr) == NULL)
        {
            // input isn't recognizable as a MAC address
            printf("invalid!\n");
        }
        else
        {
            break;
        }
    }

    printf("valid!\n");
    printf("%s\n", mac_addr);
    return 0;
}

<小时/>

听起来您一次检查一个字符，您希望立即拒绝无效字符而不等待完整的输入字符串，并且您特别希望拒绝具有小写字母或使用除冒号之外的分隔符。准确吗？我假设您这样做有自己的理由。

ispunct 函数在这里是一个转移注意力的东西。没有理由检查给定字符是否是标点符号；你真正想知道的是它是否是冒号。具体来说。您可以直接比较它们。

#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <unistd.h>
#include <termios.h>

bool is_valid(char ch, int i)
{
    if ((i + 1) % 3 == 0)
    {
        return ch == ':';
    }
    else if (ch >= '0' && ch <= '9')
    {
        return true;
    }
    else if (ch >= 'A' && ch <= 'F')
    {
        return true;
    }

    return false;
}

int main(int argc, const char *argv[])
{
    struct termios old_tio, new_tio;
    const int max_len = strlen("00:00:00:00:00:00");
    char mac_addr[max_len + 1];
    char ch = '\0';
    int i = 0;
    int ret = 0;

    /* need to modify the terminal's underlying settings, because
     * by default STDIN is buffered to support backspace, etc.
     * by switching to non-buffered input, you lose a lot of basic
     * functionality like backspace.
     * that's why it's usually recommended to just read in the entire
     * line of text and then check if it's valid at the end.
     */
    tcgetattr(STDIN_FILENO, &old_tio);
    new_tio = old_tio;
    new_tio.c_lflag &=(~ICANON);
    tcsetattr(STDIN_FILENO, TCSANOW, &new_tio);

    for (i = 0; i < max_len; i++)
    {
        ch = getchar();
        if (!is_valid(ch, i))
        {
            printf("\ninvalid!\n");
            ret = 1;
            goto exit;
        }
        mac_addr[i] = ch;
    }
    mac_addr[max_len] = '\0';

    printf("\nvalid!\n");
    printf("%s\n", mac_addr);

exit:
    /* this is important; need to reset the terminal
     * settings to their previous value before terminating.
     */
    tcsetattr(STDIN_FILENO,TCSANOW,&old_tio);
    return ret;
}