将十六进制字符串转为十六进制并返回十六进制数据长度

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

// 将十六进制字符转换为对应的数值
int hex_char_to_int(char c) 
{
    if (c >= '0' && c <= '9') {
        return c - '0';
    } else if (c >= 'a' && c <= 'f') {
        return c - 'a' + 10;
    } else if (c >= 'A' && c <= 'F') {
        return c - 'A' + 10;
    }
    return -1;
}

// 函数将十六进制字符串恢复成十六进制数据，并返回恢复后数据的长度
int hex_string_to_data(const char *hex_string, unsigned char *data) {
    int hex_length = strlen(hex_string);
    if (hex_length % 2 != 0) {
        // 十六进制字符串长度必须为偶数
        return -1;
    }

    int data_index = 0;
    for (int i = 0; i < hex_length; i += 2) {
        int high_nibble = hex_char_to_int(hex_string[i]);
        int low_nibble = hex_char_to_int(hex_string[i + 1]);
        if (high_nibble == -1 || low_nibble == -1) {
            // 包含非十六进制字符
            return -1;
        }
        // 组合高低半字节得到一个字节
        data[data_index++] = (high_nibble << 4) | low_nibble;
    }
    return data_index;
}

int main() {
    const char *hex_string = "363838323238326433313461653936616530633338366436aabbccfc";
    unsigned char data[100];

    int data_length = hex_string_to_data(hex_string, data);
    if (data_length == -1) {
        printf("输入的十六进制字符串格式错误。\n");
    } else {
        printf("恢复后数据的长度: %d\n", data_length);
        printf("恢复后的数据: ");
        for (int i = 0; i < data_length; i++) {
            printf("%02x ", data[i]);
        }
        printf("\n");
    }

    return 0;
}