test_client里的16进制数组串转化成16进制数组

1234是4个字节，要转成2个字节存储。然后发送出去。

#include<stdio.h>
#include<stdlib.h>
unsigned char *hexstr_to_hex( int length, const char *hexstr);

int main( int argc, char *argv[])
{
 
 unsigned char buffer[20];

hexstr_to_hex(4, "1234" );
//printf( "buffer is %s",buffer );

return 0;

}
/*字符长度缩短一半，16进制构成的数组转化成16进数，比如“1234”字符串要转化成12 34*/
unsigned char *hexstr_to_hex(int length, const char *hexstr)
{
    int j, k;
    unsigned char* buff;
    unsigned char* new_buff;
    int bytes_length;

    k = 0;//as counter ,when odd begin trans

    bytes_length = (length % 2) + (length / 2);

    buff =(unsigned char*)malloc(length);
    printf("hex str %s\n", hexstr);
    memcpy(buff, hexstr, length);
    printf("buff str %s\n", buff);
    printf( "buffer length is %d\n" , bytes_length );
    new_buff = malloc(bytes_length);
    memset(new_buff, 0, bytes_length);
    
    for(j = length - 1; j >= 0; j--)
    {
          printf( "------------------j = %d\n" ,j);
        if((k % 2) == 0)
        {
            printf( "+++++++++++++++j = %d, low 4 bit\n" ,j);
            if(buff[j] >= '0' && buff[j] <= '9')
            { printf( "buff[%d]=%d\n", j,buff[j] );
                new_buff[j/2] = ((buff[j] - 48) & 0x0F);
                printf( "new_buff[%d] = %d\n", j/2, new_buff[j/2] );
            } else if(buff[j] >= 'a' && buff[j] <= 'f')
            {
                new_buff[j/2] = ((buff[j] - 97 + 10) & 0x0F);
            } else if(buff[j] >= 'A' && buff[j] <= 'F')
            {
                new_buff[j/2] = ((buff[j] - 65 + 10) & 0x0F);
            } else
            {
                printf("must be hex decime\n");
                free(buff);
                free(new_buff);
                return NULL;
            }
            if( j > 0)
            {
                printf( "+++++++++++++++use j-1 = %d, high 4 bit\n" ,j-1);
                if(buff[j - 1] >= '0' && buff[j - 1] <= '9')
                {
                    new_buff[j/2] |= (((buff[j-1] - 48) << 4) & 0xF0);
                } else if(buff[j - 1] >= 'a' && buff[j - 1] <= 'f')
                {
                    new_buff[j/2] |= (((buff[j-1] - 97 + 10) << 4) & 0xF0);
                } else if(buff[j - 1] >= 'A' && buff[j - 1] <= 'F')
                {
                    new_buff[j/2] |= (((buff[j-1] - 65 + 10) << 4) & 0xF0);
                } else
                {
                    printf("must be hex decime\n");
                    free(buff);
                    free(new_buff);
                    return NULL;
                }
            }
         printf("new_buff[%d] = %d\n", j/2, new_buff[j/2] );
        }
        //when k is even number , continue:good job

        if((k % 2) == 1)
        {
            k++;
            continue;
        }
        k++;
    }
    printf( "--------------old buffer is :\n" );
    printf("%s\n", buff);
    printf( "--------------new buffer is :\n" );
    for(k = 0; k < bytes_length; k++)
    {
        printf("%x\n", new_buff[k]);
    }
    

核心用位的运算，很好！！！！值得学习！！！