Question

What I want to do is to convert a string into const char*.

Ideally I could just use “const char* myConstChar = myString.c_str()” but as my example below shows; it doesn´t work well for binary data:

#include <iostream>
#include <fstream>
#include <stdio.h>
#include <string.h>

using namespace std;

int main(){
    string myString;  // This need to be string
    ifstream infile;
const char* myConstChar;  // This need to be const char*

infile.open("binary.bin");

if(infile){
        while(getline(infile, myString)){ 
        std::cout << "Data: " << myString << " string length: "; 
            std::cout << myString.length() << "\n";
            myConstChar = myString.c_str();
            std::cout << "const char Data: " << myConstChar; 
            std::cout << " const char length: "<< strlen(myConstChar) <<"\n";
        }
    }

    infile.close();
    return 0;
}

This returns “string length: 13” and “const char length: 3”.

Apparently there are some loss of data when converting string to const char* using myString.c_str()!

How do I convert a string to const char* without losing binary data?!

Answer 1

This is almost certainly because your binary data contains zero-valued bytes. These are identical to null-terminators, which functions like strlen use to determine the end of a string.

It’s arguable that arbitrary binary data shouldn’t be treated as a string. So use std::vector<char> instead, and don’t use functions like strlen.