C++ make unsigned char * buffer from string

Question

I have this string.

char * data = "A1B2C3D4E5F6A7B8";

Here each A1 B2 C3 D4 E5 F6 A7 B8 will be bytes for unsigned char* buffer.

My concern is how to convert the data into unsigned char* buffer.

unsigned char* buffer;
buffer = (unsigned char*)data;

I will use the buffer for a parameter of a function like this to write the data into memory.

int abc(uint64_t address, buffer, uint32_t lenght);

Can anyone please give me a correct way?

`char * data = "A1B2C3D4E5F6A7B8";` is not allowed. `data` must be `const char*`. What does buffer mean here? Do you allocate memory for it somewhere? — user17732522, Oct 14 '22 at 02:43
But `buffer` now doesn't point to any allocated memory, it points to the string literal, after your edit of the question. — user17732522, Oct 14 '22 at 02:45
[**How can I convert char* buffer to unsigned char buffer**](https://stackoverflow.com/questions/34098264/how-can-i-convert-char-buffer-to-unsigned-char-buffer) seems apropos. — Andrew Henle, Oct 14 '22 at 02:45
Do you mean converting "A1B2C3D4E5F6A7B8" to {0xA1, 0xB2, 0xC3, 0xD4,...}? — thedemons, Oct 14 '22 at 02:47
What does " convert the data into unsigned char* buffer" mean? — Sam Varshavchik, Oct 14 '22 at 02:48
What error are you meet? Could you post the error code? I remember for many of system, `char` would be considered to be `unsigned`. — Xin Cheng, Oct 14 '22 at 03:12

Xin Cheng · Answer 1 · 2022-10-14T03:34:00.370

Here it is a demo about the char* buffer, unsigned char* and string.

// test.cpp
#include<iostream>
using namespace std;
void fun(unsigned char* pt) {
   cout<<*pt<<*(pt+1)<<endl;  // print first and second element
}
int main(){
    char Data[] = "abcde";       // a string with 6 elements stored in char array.
    char* data = Data;           // char pointer point to the char array
    unsigned char* buffer;       // declare an unsigned char
    buffer = (unsigned char*) data;  // buffer points to the same address data pointed.
    fun(buffer);                 // function requires an unsigned char pointer
    return 0;
}

The output

ab

To compile and run

g++ -Wall test.cpp;
./a.out

P.S.

char * data = "A1B2C3D4E5F6A7B8";

The above line would cause a warning when compiling because the string is immutable. Better changes it to char const * data = "A1B2C3D4E5F6A7B8";

Thanks for reply. but my actual concern is That A1 B2 is hexadecimal. if char * data is "0102" , it will be 0000000100000002 in binary. — KKS, Oct 14 '22 at 04:37

C++ make unsigned char * buffer from string

1 Answers1