C char数组到uint8_t数组

Question

I have a basic question regarding ac problem I'm having. My input char array would be something like:

'DABC95C1' 

and I want to make an uint8_t array out of it

0xDA 0xBC 0x95 0xC1

I have easily access to each char but I dont know how I can form 0xDA . Is there function in c or can i just cast it?

Answer 1

Use the strtoull function to convert a string to a number in a given base. Then just shift out the desired bytes. Such as:

#include <stdio.h>
#include <stdlib.h>

int main(void) {

    unsigned long long res = strtoull("DABC95C1", NULL, 16);

    printf("%hhx, %hhx, %hhx, %hhx",
        (unsigned char)res,
        (unsigned char)((res >> 8)   &  0xFF),
        (unsigned char)((res >> 16)  &  0xFF),
        (unsigned char)((res >> 24)  &  0xFF)
    );

    return 0;
}

result:

c1, 95, bc, da

Demo

Notes:

As your requirement is to get an array of bytes, you might be tempted to do something like

uint8_t *arr = (uint8_t*)&res;

But here are two caveats in this:

1) I is a strict aliasing rule violation (you can somehow to work around it by replacing uint8_t with char )
2) The order of the returned bytes will be implementation specific (endianness dependent) and thus not portable. Also note that the result is unsigned long long , so you might get extra padding zeros as either the beginning of the array or in the end of it.

Answer 2

Any size string in the chosen order. Portable digit conversion and it optimizes very well on the ASCII systems. https://godbolt.org/g/Ycah1e

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

int CharToDigit(const char c);
void *StringToTable(const char *str, const void *buff, const int order)
{
    uint8_t *ptr = (uint8_t *)buff;
    size_t len;

    int incr = order ? 1 : -1;

    if(buff && str)
    {
        len = strlen(str);

        if(len &1) return NULL;

        ptr += order ? 0 : len / 2 - 1;

        while(*str)
        {
            int d1 = CharToDigit(*str++);
            int d2 = CharToDigit(*str++);

            if(d1 == -1 || d2 == -1) return NULL;           
            *ptr = d1 * 16 + d2;
            ptr += incr;
        }
    }
    return buff;
}

int main(void) {

    int index = 0;
    char *str = "78deAc8912fF0f3B";
    uint8_t buff[strlen(str) / 2];

    StringToTable(str, buff, 0);

    printf("String: %s\nResult: ", str);
    for(index = 0; index < strlen(str) / 2; index++ )
    {
        printf("[0x%02hhx]", buff[index] );
    }
    printf("\n");

    StringToTable(str, buff, 1);

    printf("String: %s\nResult: ", str);
    for(index = 0; index < strlen(str) / 2; index++ )
    {
        printf("[0x%02hhx]", buff[index] );
    }
    printf("\n");

    return 0;
}

int CharToDigit(const char c)
{
    switch(c)
    {
        case 'a':
        case 'A':
            return 10;
        case 'b':
        case 'B':
            return 11;
        case 'c':
        case 'C':
            return 12;
        case 'd':
        case 'D':
            return 13;
        case 'e':
        case 'E':
            return 14;
        case 'f':
        case 'F':
            return 15;
        case '0':
            return 0;
        case '1':
            return 1;
        case '2':
            return 2;
        case '3':
            return 3;
        case '4':
            return 4;
        case '5':
            return 5;
        case '6':
            return 6;
        case '7':
            return 7;
        case '8':
            return 8;
        case '9':
            return 9;
        default:
            return -1;
    }
}

Answer 3

You can conver a character to an int like so

static inline int char2int(char Ch)
{
    return(Ch>='0'&&Ch<='9')?(Ch-'0'):(Ch-'A'+10); 
    //assuming correct input with no lowercase letters
}

Two characters then with

static inline 
int chars2int(unsigned char const Chars[2])
{
    return (char2int(Chars[0])<<4)|(char2int(Chars[1]));
}

And several characters by converting each pair:

static inline int char2int(char Ch)
{
    return(Ch>='0'&&Ch<='9')?(Ch-'0'):(Ch-'A'+10);
}
static inline 
int chars2int(unsigned char const Chars[2])
{
    return (char2int(Chars[0])<<4)|(char2int(Chars[1]));
}
#include <stdio.h>
#include <string.h>
#include <assert.h>
int main()
{
    char const inp[] = "DABC95C1";
    assert((sizeof(inp)-1)%2==0);
    unsigned i;
    unsigned char out[(sizeof(inp)-1)/2];
    for(i=0;i<sizeof(inp);i+=2){
        out[i/2]=chars2int((unsigned char*)inp+i);
    }
    for(i=0;i<sizeof(out);i++)
        printf("%2x\n", out[i]);
}