使用C代码实现读取文件中的hex字符串，转换为字节数组

举例说明：
ptp.txt文件中的内容为：

7a7ac0a8c80100000000003388f70002002c00000400000000000000000000000000000000000000000000000000000011111100000000000000	

解析之后为：

7a 7a c0 a8 c8 01 00 00 00 00 00 33 88 f7 00 02 
00 2c 00 00 04 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
11 11 11 00 00 00 00 00 00 00 

下面给出实现的代码：

#include <stdio.h>
#include <stddef.h>

#define PKT_ARRAY_SIZE  512
#define uint8_t  unsigned char
#define uint16_t unsigned short

static int chartoint(char ch)
{
    if(ch >= '0' && ch <= '9')          
        return ch-'0';
    if(ch >= 'A' && ch <= 'F')          
        return ch - 'A' + 10;
    if(ch >= 'a' && ch <= 'f')                      
        return ch - 'a' + 10;
    printf("Warrning: Data is wrong. %x
", ch);
    return -1;
}

static void get_hex_array_from_file(char *pkt_name, uint8_t pkt_array[PKT_ARRAY_SIZE], uint16_t *total_bytes)
{
    FILE *fp = NULL;
    char c;
    int i = 0;
    uint8_t tmp0 = 0, tmp1 = 0;
    uint16_t index = 0;

    fp = fopen(pkt_name, "r");
    if (fp == NULL) {
        printf("can not open %s
", pkt_name);
        return;
    }
    while (1) {
        c = fgetc(fp);
        if (feof(fp) || c == 0xa) {  //换行符
            if (i % 2 == 1) {
                pkt_array[index] = tmp0 & 0xFF;
                *total_bytes += 1;
            }
            break;
        }
        i += 1;
        if (i % 2 == 1) {
            tmp0 = chartoint(c);
        }
        if (i % 2 == 0) {
            tmp1 = chartoint(c);
            pkt_array[index] = ((tmp0 << 4) + tmp1) & 0xFF;
            index += 1;
            tmp0 = 0;
            tmp1 = 0;
        }
    }
    *total_bytes = index;

    fclose(fp);
}

int main(void)
{
    uint8_t pkt_array[PKT_ARRAY_SIZE] = {0};
    uint16_t total_bytes = 0;
    uint16_t i = 0;
    char *pkt_name = "ptp.txt";

    get_hex_array_from_file(pkt_name, pkt_array, &total_bytes);
    printf("total_bytes:%d
", total_bytes);
    for (i = 1; i <= total_bytes; i++) {
        printf("%02x ", pkt_array[i-1]);
        if (i % 16 == 0)
            printf("
");
    }
    printf("
");

    return 0;
}	

编译运行：