How to Display Console Output in a Windows C Program with a WinMain Entry Point?

Outputting Console Text in Windows C

Native C programs running on Windows may utilize the command-line interface to display console output. However, if the program's entry point is defined as WinMain, it's not immediately obvious how to view data printed using standard output functions like std::cout.

Solution:

There are several approaches to achieve console output in this scenario:

1. Utilizing a Redirect Function:

Implement a custom redirection function that intercepts standard I/O streams and routes them to the console. Here's an example using the Win32 API:

guicon.cpp

#include <windows.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>
#include <iostream>
#include <fstream>
using namespace std;

void RedirectIOToConsole() {
  int hConHandle;
  long lStdHandle;
  FILE *fp;

  AllocConsole();
  GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &coninfo);
  coninfo.dwSize.Y = MAX_CONSOLE_LINES;
  SetConsoleScreenBufferSize(GetStdHandle(STD_OUTPUT_HANDLE), coninfo.dwSize);

  lStdHandle = (long)GetStdHandle(STD_OUTPUT_HANDLE);
  hConHandle = _open_osfhandle(lStdHandle, _O_TEXT);
  fp = _fdopen(hConHandle, "w");
  *stdout = *fp;
  setvbuf(stdout, NULL, _IONBF, 0);

  lStdHandle = (long)GetStdHandle(STD_INPUT_HANDLE);
  hConHandle = _open_osfhandle(lStdHandle, _O_TEXT);
  fp = _fdopen(hConHandle, "r");
  *stdin = *fp;
  setvbuf(stdin, NULL, _IONBF, 0);

  lStdHandle = (long)GetStdHandle(STD_ERROR_HANDLE);
  hConHandle = _open_osfhandle(lStdHandle, _O_TEXT);
  fp = _fdopen(hConHandle, "w");
  *stderr = *fp;
  setvbuf(stderr, NULL, _IONBF, 0);

  ios::sync_with_stdio();
}

Then, include this function in your program and call it before using standard output functions.

2. Redirecting Console Output to a File:

Another option is to redirect console output to a file, which can then be viewed using a text editor. This can be done by modifying the program's command line:

program.exe 1>output.txt 2>&1

In this example, standard output and standard error are redirected to the "output.txt" file.

3. Using Conditional Compilation:

If your program specifically targets development or debugging environments, you can use conditional compilation to include console output only when necessary. For instance, you can wrap your console output statements in #ifdef _DEBUG blocks.

Example Implementation:

test.cpp

#include <iostream>

#ifdef _DEBUG
int main() {
  std::cout << "Hello, world!" << std::endl;
  return 0;
}
#endif

By default, this program will not output anything. However, when compiled with the _DEBUG preprocessor macro defined, it will print "Hello, world!" to the console.

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