Using c.str to convert from string to cstring

Question

I am practicing some work with cstring and string. Going from string to cstring using c_str() I get an incompatible data type compile error. For example this is the code that gives said error:

string str = "StackOverFlow";
char inCstring[20]{};
inCstring = str.c_str();

Any ideas?

Try using char* inCstring; instead of char inCstring[20]{};. — phantom
– phantom, Commented Jan 28, 2016 at 2:36
If you found a solution, you should post it as an answer, not in the question. — Barmar
– Barmar, Commented Jan 28, 2016 at 3:08

Vicente Cunha · Accepted Answer · 2016-01-28 05:08:41Z

3

The problem is that str.c_str() returns a const char*, and you are trying to pass it to a char*. Use strcpy to get your expected result:

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

using namespace std;

int main()
{
    string str = "StackOverFlow";
    char inCstring[20];

    strcpy(inCstring, str.c_str());

    cout << "str: " << str << endl;
    cout << "inCstring: " << inCstring << endl;

    return 0;
}

edited Jan 28, 2016 at 5:08

answered Jan 28, 2016 at 2:54

Vicente Cunha

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4 Comments

Vicente Cunha Over a year ago

Just noticed OP figured out the same answer as "Method B". I do not believe anything is wrong regarding "programming style", only to it not being a 'lvalue =' assignment. Method A is lacking because the new cstring is const.

M.M Over a year ago

The problem is that he was trying to assign to an array (char [] type) , not char * .

Vicente Cunha Over a year ago

@M.M That is true. Yet it should be noted that in the sample code, directly swapping char inCstring[20]; to char* inCstring; causes a segmentation fault.

Vicente Cunha Over a year ago

And attempting the lines char* inCstring; inCstring = str.c_str(); produces invalid conversion error by the compiler.

amol_Dee_sandwich · Accepted Answer · 2016-01-28 05:09:26Z

So I have figured out two ways to accomplish this.
First, it is important to remember that you can't assign to a whole array, meaning it is necessary to specify the element of the array to assign to. Attempting to assign a string to char array simply will not work for this reason.
That being said, by specifying the element it would be possible to assign a character in a specific element of a char array.
Below are two methods that accomplish a string to cstring(string to char array) "conversion". Please see answer by Vincent for complete code. I have found Method B better since I would like to have max size on my character array.

Method A:

string str = "StackOverFlow";
const char* inCstring;
inCstring = str.c_str();

Method B:

string str = "StackOverFlow";
char inCstring[20]{};

Then use strcpy

strcpy(inCstring, str.c_str());

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