Category: C/C++

Simple POSIX Semaphore Library for Windows

dandenongs 1889

I had a recent need to control access of one of my programs to a hardware device – basically the hardware can only handle a certain number of simultaneous connections before it starts returning garbage. POSIX semaphores are a really elegant way of handling this as you just create a semaphore and then put a semi_wait call before every critical code section and a sem_post call at the end of the critical code. This way you can control the number of simultaneous calls of the critical code no matter how many parallel processes or threads are running.

The only problem with POSIX semaphores is they are not natively supported on Windows (Windows has a entirely different semaphore system). Since my program is cross-platform I wanted a simple Windows-compatible POSIX semaphore library I could just drop in on my Windows builds and avoid a whole series of #ifdef #else conditionals. I managed to find a full Windows POSIX thread library (libpthread), but it was way more complex than what I needed and it does not build on Windows XP (I unfortunately still need to support Windows XP/2003). I was able to use the library as a starting point for making a very simple POSIX semaphore library. My cut-down library provides a simple drop in replacement for all the POSIX semaphore functions on Windows and just requires the inclusion of the header file in any project you might want to use it in. It is not identical to semaphores on linux, but it does the job.

You can download the simple windows semaphore library from my github repository. I hope it is of help for someone else.

Tracking down global variables in C code

I recently had the fun job of making some complex legacy C code (200,000+ lines) thread safe. Of course there were globals spread through the code so finding them all turned into a massive easter egg hunt. The initial problem was how to track them all down. If you ever have this fun job here are the steps I used.

1. I searched for the word “global”. If the person who wrote the code took care then all the global variables will have been commented as such (ha ha). Maybe surprisingly this did managed to find around 50% of the globals – while not perfect, it was a good start. I also found a few more unlabelled globals by searching for “thread-safe” and “thread” since some of the non-thread safe code was actually commented as being not thread-safe (I wish it all had been).

2. I next opened the .map file (generated by Visual Studio in debug mode) and looked for any “common” class variables (these are found down towards the bottom of the .map file). This process managed to shake out another 40% of the globals.

3. The last 5% of globals I found by doing a manual search through the entire code base for the “static” keyword. I of course then had to then trawl through several thousand static function declarations, but the last of the globals were in here too.

The most interesting thing about this painful exercise is how often people use globals when they are not really needed. 90% of the globals were being used only two or three times and were able to be made thread safe with very little code change. Of course the last 10% were used in more than 100 locations spread throughout the entire code base so the whole thread safe conversion exercise was not easy.

To keep the required code change to a minimum (I am very reluctant to make major structural changes to complex code even if I have written it) I solved the problem by just packaging up the difficult globals into a thread-safe strut declared in the main entry function and passed the pointer to this strut into each of the functions that were using the globals. While not a trivial job, this approach avoided disturbing code I knew was working well and which would have taken months to re-write.

Base32 implementation of the Damm error detection algorithm in C

The Damm algorithm is a fantastic check digit algorithm that detects all single-digit errors and all adjacent transposition errors. It detects all occurrences of altering one single digit and all occurrences of transposing two adjacent digits, the two most frequent transcription errors. The Damm algorithm also has the benefit that prepending leading base encoding zeros does not affect the check digit so you can use it on fixed size strings. All in all it is a great algorithm for checking if there have been any user errors when entering a number.

The only problem with the Damm algorithm is that all the current implementations are base 10 (0-9) only. I wanted to be able to use it to check alpha-numerical strings (passwords) so I wrote a base32 implementation of the Damm algorithm in C/C++. With the commonly confused characters (0/o and 1/l/i) avoided in the base32 encoding you can make a rather nice password checker. Any desired encoding scheme with 32 characters (or less) can be used.

I use the damn32 program in a bash one-liner to generate 10 (9 + the damn check) character password strings. You can make longer or shorter strings by changing the head -c switch.

# openssl rand -base64 50 | tr -dc '23456789abcdefghjkmnpqrstuvwxyz' | head -c9 | xargs damn32

Here is the code for damn32.c. It can be compiled with gcc using:

# gcc damn32.c -o damn32

I will to port this to javascript and php when I get the chance, but if someone wants to do it now I am happy to link to your code or post it here.

Edit.Thanks Michael for pointing out that due to some stupidity on my behalf the code got called damn.c not damm.c – I have updated the post title, but I will leave the code as is as a reminder to be more careful next time :)


#include 

/*
    Base32 implementation of the Damm error detection algorithm in C

    Copyright (c) 2014, Daniel Tillett
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice, this
    list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright notice,
    this list of conditions and the following disclaimer in the documentation
    and/or other materials provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
    ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
    WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
    DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
    ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
    (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
    ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
    SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

    BACKGROUND
    The Damm algorithm is a check digit algorithm that detects all single-digit errors 
    and all adjacent transposition errors.
 
    It detects all occurrences of altering one single digit and all occurrences of 
    transposing two adjacent digits, the two most frequent transcription errors.
 
    The Damm algorithm has the benefit that it makes do without the dedicatedly 
    constructed permutations and its position specific powers being inherent in the 
    Verhoeff scheme. Prepending leading base encoding zeros does not affect the check digit.
    https://en.wikipedia.org/wiki/Damm_algorithm
*/

/*
    A base32 (or less) encoding.
 
    With this example encoding the base 0 is '2' and contains 31 characters that avoids 
    using characters that could be confused with each other (i.e. 0/o or 1/i/l).
 
    The encoding can be any scheme with 32 or less characters. To change the encoding
    update encodeLen and base32 to the desired values. In this example on 31 characters 
    are used
*/
const int encodeLen = 31;
const char base32[encodeLen] = "23456789abcdefghjkmnpqrstuvwxyz";

/*
    Returns index position of the base32 digit if the digit exists in the base32 string
    or encodeLen if not.
*/
int base32Index(char p) {
	int i;

	for (i = 0; i < encodeLen; i++) {
		if (p == base32[i]) {
			break;
			}
		}

	return i;
	}

/*
    Damn algorithm base32 check digit calculator.
 
    Returns the base32 check digit defined by the base32 string or '-' if the base32
    number contains a character that is not defined in the base32 string.
    
    Input must be a null terminated C string.
*/
char damm32Encode(char *code) {
	int i, interim = 0;
	char *p;
	/*
	    WTA quasigroup matrix of order 32
	    http://stackoverflow.com/questions/23431621/extending-the-damm-algorithm-to-base-32
	    This was constructed according to Damm Lemma 5.2 by Michael 
	    (http://stackoverflow.com/users/3625116/michael)
	    I suspect this Michael is the Michael Damm, but I really don't know :)
	*/
	char damm32Matrix[32][32] = {
			{ 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 3, 1, 7, 5, 11, 9, 15, 13, 19, 17, 23, 21, 27, 25, 31, 29},
			{ 2, 0, 6, 4, 10, 8, 14, 12, 18, 16, 22, 20, 26, 24, 30, 28, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31},
			{ 4, 6, 0, 2, 12, 14, 8, 10, 20, 22, 16, 18, 28, 30, 24, 26, 7, 5, 3, 1, 15, 13, 11, 9, 23, 21, 19, 17, 31, 29, 27, 25},
			{ 6, 4, 2, 0, 14, 12, 10, 8, 22, 20, 18, 16, 30, 28, 26, 24, 5, 7, 1, 3, 13, 15, 9, 11, 21, 23, 17, 19, 29, 31, 25, 27},
			{ 8, 10, 12, 14, 0, 2, 4, 6, 24, 26, 28, 30, 16, 18, 20, 22, 11, 9, 15, 13, 3, 1, 7, 5, 27, 25, 31, 29, 19, 17, 23, 21},
			{10, 8, 14, 12, 2, 0, 6, 4, 26, 24, 30, 28, 18, 16, 22, 20, 9, 11, 13, 15, 1, 3, 5, 7, 25, 27, 29, 31, 17, 19, 21, 23},
			{12, 14, 8, 10, 4, 6, 0, 2, 28, 30, 24, 26, 20, 22, 16, 18, 15, 13, 11, 9, 7, 5, 3, 1, 31, 29, 27, 25, 23, 21, 19, 17},
			{14, 12, 10, 8, 6, 4, 2, 0, 30, 28, 26, 24, 22, 20, 18, 16, 13, 15, 9, 11, 5, 7, 1, 3, 29, 31, 25, 27, 21, 23, 17, 19},
			{16, 18, 20, 22, 24, 26, 28, 30, 0, 2, 4, 6, 8, 10, 12, 14, 19, 17, 23, 21, 27, 25, 31, 29, 3, 1, 7, 5, 11, 9, 15, 13},
			{18, 16, 22, 20, 26, 24, 30, 28, 2, 0, 6, 4, 10, 8, 14, 12, 17, 19, 21, 23, 25, 27, 29, 31, 1, 3, 5, 7, 9, 11, 13, 15},
			{20, 22, 16, 18, 28, 30, 24, 26, 4, 6, 0, 2, 12, 14, 8, 10, 23, 21, 19, 17, 31, 29, 27, 25, 7, 5, 3, 1, 15, 13, 11, 9},
			{22, 20, 18, 16, 30, 28, 26, 24, 6, 4, 2, 0, 14, 12, 10, 8, 21, 23, 17, 19, 29, 31, 25, 27, 5, 7, 1, 3, 13, 15, 9, 11},
			{24, 26, 28, 30, 16, 18, 20, 22, 8, 10, 12, 14, 0, 2, 4, 6, 27, 25, 31, 29, 19, 17, 23, 21, 11, 9, 15, 13, 3, 1, 7, 5},
			{26, 24, 30, 28, 18, 16, 22, 20, 10, 8, 14, 12, 2, 0, 6, 4, 25, 27, 29, 31, 17, 19, 21, 23, 9, 11, 13, 15, 1, 3, 5, 7},
			{28, 30, 24, 26, 20, 22, 16, 18, 12, 14, 8, 10, 4, 6, 0, 2, 31, 29, 27, 25, 23, 21, 19, 17, 15, 13, 11, 9, 7, 5, 3, 1},
			{30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, 0, 29, 31, 25, 27, 21, 23, 17, 19, 13, 15, 9, 11, 5, 7, 1, 3},
			{ 3, 1, 7, 5, 11, 9, 15, 13, 19, 17, 23, 21, 27, 25, 31, 29, 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30},
			{ 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 2, 0, 6, 4, 10, 8, 14, 12, 18, 16, 22, 20, 26, 24, 30, 28},
			{ 7, 5, 3, 1, 15, 13, 11, 9, 23, 21, 19, 17, 31, 29, 27, 25, 4, 6, 0, 2, 12, 14, 8, 10, 20, 22, 16, 18, 28, 30, 24, 26},
			{ 5, 7, 1, 3, 13, 15, 9, 11, 21, 23, 17, 19, 29, 31, 25, 27, 6, 4, 2, 0, 14, 12, 10, 8, 22, 20, 18, 16, 30, 28, 26, 24},
			{11, 9, 15, 13, 3, 1, 7, 5, 27, 25, 31, 29, 19, 17, 23, 21, 8, 10, 12, 14, 0, 2, 4, 6, 24, 26, 28, 30, 16, 18, 20, 22},
			{ 9, 11, 13, 15, 1, 3, 5, 7, 25, 27, 29, 31, 17, 19, 21, 23, 10, 8, 14, 12, 2, 0, 6, 4, 26, 24, 30, 28, 18, 16, 22, 20},
			{15, 13, 11, 9, 7, 5, 3, 1, 31, 29, 27, 25, 23, 21, 19, 17, 12, 14, 8, 10, 4, 6, 0, 2, 28, 30, 24, 26, 20, 22, 16, 18},
			{13, 15, 9, 11, 5, 7, 1, 3, 29, 31, 25, 27, 21, 23, 17, 19, 14, 12, 10, 8, 6, 4, 2, 0, 30, 28, 26, 24, 22, 20, 18, 16},
			{19, 17, 23, 21, 27, 25, 31, 29, 3, 1, 7, 5, 11, 9, 15, 13, 16, 18, 20, 22, 24, 26, 28, 30, 0, 2, 4, 6, 8, 10, 12, 14},
			{17, 19, 21, 23, 25, 27, 29, 31, 1, 3, 5, 7, 9, 11, 13, 15, 18, 16, 22, 20, 26, 24, 30, 28, 2, 0, 6, 4, 10, 8, 14, 12},
			{23, 21, 19, 17, 31, 29, 27, 25, 7, 5, 3, 1, 15, 13, 11, 9, 20, 22, 16, 18, 28, 30, 24, 26, 4, 6, 0, 2, 12, 14, 8, 10},
			{21, 23, 17, 19, 29, 31, 25, 27, 5, 7, 1, 3, 13, 15, 9, 11, 22, 20, 18, 16, 30, 28, 26, 24, 6, 4, 2, 0, 14, 12, 10, 8},
			{27, 25, 31, 29, 19, 17, 23, 21, 11, 9, 15, 13, 3, 1, 7, 5, 24, 26, 28, 30, 16, 18, 20, 22, 8, 10, 12, 14, 0, 2, 4, 6},
			{25, 27, 29, 31, 17, 19, 21, 23, 9, 11, 13, 15, 1, 3, 5, 7, 26, 24, 30, 28, 18, 16, 22, 20, 10, 8, 14, 12, 2, 0, 6, 4},
			{31, 29, 27, 25, 23, 21, 19, 17, 15, 13, 11, 9, 7, 5, 3, 1, 28, 30, 24, 26, 20, 22, 16, 18, 12, 14, 8, 10, 4, 6, 0, 2},
			{29, 31, 25, 27, 21, 23, 17, 19, 13, 15, 9, 11, 5, 7, 1, 3, 30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, 0}
		};

	for (p = code; *p != '\0'; ++p) {
		i = base32Index(*p);

		if (i == encodeLen) {
			return '-';
			}

		interim = damm32Matrix[interim][i];
		}

	return base32[interim];
	}

/*
    Damm32 Check
 
    Returns 1 if the base32 number is error free and 0 if it contains an error
    or the last digit is not equal to the error check digit.
*/
int damm32Check(char *code) {
	return (damm32Encode(code) == base32[0]) ? 1 : 0;
	}

/*
    Prints to stdout the input base32 number, the base32 check digit, and the damm32 check result.
*/
int main(int argc, char **argv) {
	if (argc == 2 && argv[1]) {
		printf("Input: %s\nCheck Digit: %c\nChecked: %d\n", argv[1], damm32Encode(argv[1]), damm32Check(argv[1]));
		return 1;
		}

	else {
		printf("Usage: damm32 [base32 number]\n");
		return 0;
		}
	}

setrlimit not raising a signal with SIGXCPU

I ran into a unusual linux bug of late using RLIMIT_CPU to kill zombie processes that ran for longer than 15 seconds. The basic code I was using was:

struct rlimit rl;
memset(&rl, 0, sizeof(rl));
/* Set a CPU limit of 15 second. */
rl.rlim_cur = 15;
setrlimit(RLIMIT_CPU, &rl);
/* CPU Time exceeded */
signal(SIGXCPU, catchSignal);

This worked fine when I original wrote it a few years ago, but I noticed of late that I was spawning a large number of zombie processes that were not being trapped by SIGXCPU. After tearing my hair out all day trying to work out why, I noticed that this was only occurring on my CentOS 6.5 development box (Linux version 2.6.32). It turns out that there was a bug in the implementation of setrlimit before 2.6.17 that led a RLIMIT_CPU limit of 0 to be wrongly treated as “no limit” (like RLIM_INFINITY). Since 2.6.17 this is now treated as a limit of 1 second. Since I was setting rlim_max to 0 via memset meant that I was now effectively setting rlim_max to less than rlim_cur.

The solution is really simple – just ensure that you set rlim_max (hard limit) as well as rlim_cur (soft limit).

struct rlimit rl;
/* Set a CPU soft limit of 15 second and hard limit of 20 seconds */
rl.rlim_cur = 15;
rl.rlim_max = 20;
setrlimit(RLIMIT_CPU, &rl);
/* CPU Time exceeded */
signal(SIGXCPU, catchSignal);

How to create a Windows program that works both as a GUI and console application

It would be very nice to be able to make Windows applications that can act as either a GUI or console application depending on how they are used (i.e. act as a GUI application if double clicked in Windows Explorer or as a console application if called from a cmd.exe window).

Unfortunately the way Windows work, each exe application has field in the PE header that specifies which subsystem it should run under. This is set in Visual Studio by using one of the linker SUBSYSTEM option (i.e. Windows or Console). The subsystem is used by the Windows kernel to set up the execution environment for the application. If the application is built using SUBSYSTEM/Console then the kernel will connect the application to the parent console and the application’s stdout, stderr and stdin will be redirected to the parent console. If the program is built as a GUI application then the application detaches from the parent console and all output to stdout and stderr are are lost – basically the program runs, but doesn’t output anything to the parent console window.

People have attempted various hacks over the years to solve this problem. One solution proposed was to compile the program as a Windows application and then edit the PE header to mark the program as using the Console subsystem. The downside of this approach is it flashes a Console window on the screen when run as a GUI application that looks pretty unprofessional. The second hack commonly used is to create two separate binaries, for example, a myuselessprogram.com and myuselessprogram.exe. The .com version is built as a Console application while the .exe is built as Windows application. When you run myuselessprogram the Windows probing rule runs the .com version first and if there is nothing on the command line then the .com version calls the .exe Windows version. While both these approaches work, they are to say less than ideal.

A better approach is use the WINAPI AttachConsole function to attach the application to the parent console and then redirect stdout, stdin and stderr back to the parent console. This actually works very well except that when the application exits the parent console can’t detect this and hence release the command prompt. The end result is the parent console just sits there until the user presses the “enter” key.

There is no really elegant solution to this problem, but as applications can simulate the keyboard being used, a simple solution is to call the SendInput API function with the “enter” key just before the application exits. This simulates the user pressing the enter key and hence releases the command prompt.

To show how this approach works I have written a small test application (see below). The main limitations is that AttachConsole is only available on Windows XP and above. It does works under Cygwin which is nice.

Update. I have added a check to make sure that the console window is in focus before sending the enter key. It is a good check to make if you are running your console program in a background script or else you will end up with lots of “enter” key presses in whatever application you actually have in focus – lots of fun if you are working on the documentation while a script runs in the background :)

Update 2. Contrary to what has been posted on Stack Overflow this approach works with STDIN too. I don’t have any need to capture STDIN with my application (just the command line parameters), but all you need to do to capture stdin is treat STDIN as is done for STDOUT (i.e just redirect STDIN to the console) in the attachOutputToConsole function.

Update 3. This is MIT licensed if this is important to you :)

Update 4. Microsoft has broken the old approach I was using in VS2015. I have updated the code to use a different way of attaching STDOUT and STRERR to the parent console. This code works with VS2015 and all earlier compliers I was able to test (VS2013, VS2008, VS2005).

/*

 Copyright (c) 2013, 2016 Daniel Tillett
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:
 
 1. Redistributions of source code must retain the above copyright notice, this
 list of conditions and the following disclaimer.
 2. Redistributions in binary form must reproduce the above copyright notice,
 this list of conditions and the following disclaimer in the documentation
 and/or other materials provided with the distribution.
 
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

*/

#define WINVER 0x0501 // Allow use of features specific to Windows XP or later.
#define _WIN32_WINNT 0x0501
#define WIN32_LEAN_AND_MEAN
#include "windows.h"
#include "io.h"
#include "fcntl.h"
#include "stdio.h"
#include "stdlib.h"
#pragma comment(lib, "User32.lib")

// Attach output of application to parent console
static BOOL attachOutputToConsole(void) {
HANDLE consoleHandleOut, consoleHandleError;

if (AttachConsole(ATTACH_PARENT_PROCESS)) {
  // Redirect unbuffered STDOUT to the console
  consoleHandleOut = GetStdHandle(STD_OUTPUT_HANDLE);
  if (consoleHandleOut != INVALID_HANDLE_VALUE) {
    freopen("CONOUT$", "w", stdout);
    setvbuf(stdout, NULL, _IONBF, 0);
    }
  else {
    return FALSE;
    }
  // Redirect unbuffered STDERR to the console
  consoleHandleError = GetStdHandle(STD_ERROR_HANDLE);
  if (consoleHandleError != INVALID_HANDLE_VALUE) {
    freopen("CONOUT$", "w", stderr);
    setvbuf(stderr, NULL, _IONBF, 0);
    }
  else {
    return FALSE;
   }
  return TRUE;
  }
//Not a console application
return FALSE;
}

// Send the "enter" to the console to release the command prompt 
// on the parent console
static void sendEnterKey(void) {
 INPUT ip;
 // Set up a generic keyboard event.
 ip.type = INPUT_KEYBOARD;
 ip.ki.wScan = 0; // hardware scan code for key
 ip.ki.time = 0;
 ip.ki.dwExtraInfo = 0;

 // Send the "Enter" key
 ip.ki.wVk = 0x0D; // virtual-key code for the "Enter" key
 ip.ki.dwFlags = 0; // 0 for key press
 SendInput(1, &ip, sizeof(INPUT));

 // Release the "Enter" key
 ip.ki.dwFlags = KEYEVENTF_KEYUP; // KEYEVENTF_KEYUP for key release
 SendInput(1, &ip, sizeof(INPUT));
}

int WINAPI WinMain(HINSTANCE hInstance, 
HINSTANCE hPrevInstance, 
PSTR lpCmdLine, 
INT nCmdShow) {
int argc = __argc;
char **argv = __argv;
UNREFERENCED_PARAMETER(hInstance);
UNREFERENCED_PARAMETER(hPrevInstance);
UNREFERENCED_PARAMETER(lpCmdLine);
UNREFERENCED_PARAMETER(nCmdShow);
BOOL console;
int i;

//Is the program running as console or GUI application
console = attachOutputToConsole();

if (console) {
    // Print to stdout
    printf("Program running as console application\n");
    for (i = 0; i < argc; i++) {
         printf("argv[%d] %s\n", i, argv[i]);
         }

    // Print to stderr
    fprintf(stderr, "Output to stderr\n");
    }
else {
    MessageBox(NULL, "Program running as Windows GUI application",
    "Windows GUI Application", MB_OK | MB_SETFOREGROUND);
}

// Send "enter" to release application from the console
// This is a hack, but if not used the console doesn't know the application has
// returned. The "enter" key only sent if the console window is in focus.
if (console && (GetConsoleWindow() == GetForegroundWindow())){
    sendEnterKey();
    }
return 0;
}

Installing Splint on Mac OSX

Splint is a really useful utility to check your source code, but it doesn’t seem to be installed by default on MacOS X. It is not too difficult to download the source and install except for the minor issue that it doesn’t build. The good news is it doesn’t take much to fix the build problem. Here are the instructions.

  1. Download the source from http://www.splint.org/downloads/splint-3.1.2.src.tgz
  2. Open the .tgz file by double clicking.
  3. Open a terminal window and cd to the splint-3.1.2 folder
  4. Configure by using sudo ./configure and enter your password
  5. Open the osd.c file using nano src/osd.c
  6. Scroll down to around line 500 and change the line __pid_t pid = getpid (); to pid_t pid = getpid (); then save the file (control-x).
  7. Type sudo make install to install splint

You should now be able to use splint (eg splint foo.c) and have a look at how many little issues are in your code :) It will fail a few of the tests, but it appears to still work.

Edit Sept 2017. This is a pretty old post. My advice is use brew to install splint.