C++ Convert Char Array To Hex String

Question

I'm working on a very old machine in which the SDK I use to compile my C++ executable's does not support string, so I need to work with char arrays.

This code works fine for converting a string to hex

std::string string_to_hex(const std::string& input)
{
    static const char* const lut = "0123456789ABCDEF";
    size_t len = input.length();

    std::string output;
    output.reserve(2 * len);
    for (size_t i = 0; i < len; ++i)
    {
        const unsigned char c = input[i];
        output.push_back(lut[c >> 4]);
        output.push_back(lut[c & 15]);
    }
    return output;
}

But the function works with the string data type, which I cannot use.

I've tried using this as well, but to no avail.

char *hextostrTest(char *hexStr)
{
    size_t len = strlen(hexStr);
    int k = 0;
    if (len & 1) return NULL;

    char* output = new char[(len / 2) + 1];
    for (size_t i = 0; i < len; i += 2)
    {
        output[k++] = (((hexStr[i] >= 'A') ? (hexStr[i] - 'A' + 10) : (hexStr[i] - '0')) << 4) |
            (((hexStr[i + 1] >= 'A') ? (hexStr[i + 1] - 'A' + 10) : (hexStr[i + 1] - '0')));
    }
    output[k] = '\0';
    return output;
}

@HyunIKim Like mentioned above, I'm unable to use the string data type due to this old broken SDK, but it is the only SDK available for the old machine I am working with so I need to deal with it. I can only work with char arrays — Coder1337
– Coder1337, Commented Feb 22, 2018 at 2:43
why you don't just replace the string part but rewrite the whole function? — apple apple
– apple apple, Commented Feb 22, 2018 at 2:46
@appleapple Because porting the reserve() and push_back() functions to work with char arrays would be a pain in the ass. — Coder1337
– Coder1337, Commented Feb 22, 2018 at 2:52
you replace reserve() with alloc memory, push_back is pretty easy to implement. Anyway, if you have hextostr with std::string, post it. string_to_hex helps nothing — apple apple
– apple apple, Commented Feb 22, 2018 at 2:53

Marker · Accepted Answer · 2018-02-22 02:56:22Z

2

Something very similar:

const char* string_to_hex(const char *str, char *hex, size_t maxlen)
{
    static const char* const lut = "0123456789ABCDEF";

    if (str == NULL) return NULL;
    if (hex == NULL) return NULL;
    if (maxlen == 0) return NULL;

    size_t len = strlen(str);

    char *p = hex;

    for (size_t i = 0; (i < len) && (i < (maxlen-1)); ++i)
    {
        const unsigned char c = str[i];
        *p++ = lut[c >> 4];
        *p++ = lut[c & 15];
    }

    *p++ = 0;

    return hex;
}

int main()
{
    char hex[20];
    const char *result = string_to_hex("0123", hex, sizeof(hex));
    return 0;
}

answered Feb 22, 2018 at 2:56

Marker

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Comments

aram · Accepted Answer · 2018-02-22 02:51:41Z

Just use the same function for std::string but with char *,

#include <iostream>                                                    
#include <cstdlib>                                                     
#include <cstring>                                                     
#include <string>                                                      

using namespace std;                                                   

char *string_to_hex(char *input) {                                     
    static const char *const lut = "0123456789ABCDEF";                 
    size_t len = strlen(input);                                        
    int k = 0;                                                         
    if (len & 1)                                                       
        return NULL;                                                   

    char *output = new char[(len / 2) + 1];                            

    for (size_t i = 0, j = 0; i < len; i++, j += 2) {                  
        const unsigned char c = input[i];                              
        output[j]     = lut[c >> 4];                                       
        output[j + 1] = lut[c & 15];                                   
    }                                                                  

    return output;                                                     
}                                                                      

std::string string_to_hex(const std::string &input) {                  
    static const char *const lut = "0123456789ABCDEF";                 
    size_t len = input.length();                                       

    std::string output;                                                
    output.reserve(2 * len);                                           
    for (size_t i = 0; i < len; ++i) {                                 
        const unsigned char c = input[i];                              
        output.push_back(lut[c >> 4]);                                 
        output.push_back(lut[c & 15]);                                 
    }                                                                  
    return output;                                                     
}                                                                      

int main() {                                                           
    string test = "Test";                                              
    std::string res(string_to_hex(test.c_str()));                      
    cout << res << endl;                                               
    res = string_to_hex(test);                                         
    cout << res << endl;                                               
}

Hyun I Kim · Accepted Answer · 2018-02-22 03:09:10Z

0

Two codes you clipped look like opposite codes.

char* string_to_hex(const char* input) {
    static const char* const lut = "0123456789ABCDEF";
    size_t len = strlen(input);

    char* output = new char[len*2+1];
    int index = 0;
    for(size_t i = 0; i < len; ++i) {
        const unsigned char c = input[i];
        output[index++] = lut[c >> 4];
        output[index++] = lut[c & 15];
    }
    output[index] = '\0';
    return output;
}

This is the string -> char* version of the first code.

answered Feb 22, 2018 at 3:09

Hyun I Kim

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