Converting _TCHAR* to char*

Question

I'm trying to get a simple OpenCV sample working in C++ on Windows and my C++ is more than rusty.

The sample is fairly simple:

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main( int argc, char** argv )
{
    if( argc != 2)
    {
        cout <<" Usage: display_image ImageToLoadAndDisplay" << endl;
        return -1;
    }
    Mat image;
    image = imread(argv[1], IMREAD_COLOR); // Read the file
    if(! image.data )                      // Check for invalid input
    {
        cout <<  "Could not open or find the image" << std::endl ;
        return -1;
    }
    namedWindow( "Display window", WINDOW_AUTOSIZE ); // Create a window for display.
    imshow( "Display window", image );                // Show our image inside it.
    waitKey(0); // Wait for a keystroke in the window
    return 0;
}

When I make a new simple C++ console application (with ATL) in Visual Studio 2012 I get a different template for main:

int _tmain( int argc, _TCHAR* argv[] )

So before I send the filename to OpenCV's imread function I need to convert the _TCHAR* arg[1] to a char*. Using a simple filename, 'opencv-logo.jpg', from the memory in the memory window I can see that the _TCHAR are taking two bytes each

o.p.e.n.c.v.-.l.o.g.o...j.p.g...
6f 00 70 00 65 00 6e 00 63 00 76 00 2d 00 6c 00 6f 00 67 00 6f 00 2e 00 6a 00 70 00 67 00 00 00

Following the conversion recommendation in another answer I am trying to use ATL 7.0 String Conversion Classes and Macros by inserting the following code:

char* filename = CT2A(argv[1]);

But the resulting memory is a mess, certainly not 'opencv-logo.jpg' as an ascii string:

fe fe fe fe fe fe fe fe fe fe ...
þþþþþþþþþþ ...

Which conversion technique, function, or macro should I be using?

(N.B. This may be a related question but I cannot see how to apply the answer here.)

Answer 1

The quickest solution is to just change the signature to the standard one. Replace:

int _tmain( int argc, _TCHAR* argv[] )

With

int main( int argc, char *argv[] )

This does mean on Windows that the command line arguments get converted to the system's locale encoding and since Windows doesn't support UTF-8 here not everything converts correctly. However unless you actually need internationalization then it may not be worth your time to do anything more.