How to add a Makefile post-build step

24 September, 2010 § 1 Comment

I spend most of my time working in Visual Studio and like its ability for performing post-build steps. These can be used to copy files, register DLLs, or run unit tests.

In my work at MSU I need to use a makefile and have been writing my code test-first. As such, I found I was spending a lot of time typing make and then typing ./runTests. Ideally, I could just have the tests run automatically after each build.

Looking around on the internet for quick steps to add a post-build step to make wasn’t so fruitful. I ran in to a bunch of old forum posts that mentioned Visual Studio-generated makefiles with post-build steps. A little thinking about the idea sprang the solution straight to mind.

It turns out it is really simple and quite intuitive. Here’s my current makefile:

CC=g++
CFLAGS=-c -Wall -pedantic-errors -Wextra -Wunused -Werror

all: findRoute findRoute-test runTests

rebuild: clean all

runTests: findRoute-test
	./findRoute-test.exe

findRoute: main.o cities.o flight_charges.o traffic_controller.o
	$(CC) main.o cities.o flight_charges.o traffic_controller.o -o findRoute

findRoute-test: main-test.o cities.o flight_charges.o traffic_controller.o
	$(CC) main-test.o cities.o flight_charges.o traffic_controller.o -o findRoute-test

main.o: main.cpp
	$(CC) $(CFLAGS) main.cpp

cities.o: cities.cpp
	$(CC) $(CFLAGS) cities.cpp

flight_charges.o: flight_charges.cpp
	$(CC) $(CFLAGS) flight_charges.cpp

traffic_controller.o: traffic_controller.cpp
	$(CC) $(CFLAGS) traffic_controller.cpp

main-test.o: main-test.cpp
	$(CC) $(CFLAGS) main-test.cpp

clean:
	rm -rf *o findRoute*

The runTests step above states that the findRoute-test step is a prerequisite. If that step passes, then it simply executes the next line, that being the test executable.

I found this very intuitive as it is no different than any other executable like the compiler. I hope this helps someone else who is thinking of doing the same or a variation.

Do you see anything above that could be improved? I love getting comments that help me get better.

Initializing an array in C++

16 June, 2010 § 6 Comments

Most people know about member initialization lists in C++. Initialization lists allow you to initialize a variable when the class is instantiated, versus assigning a value within the constructor.

Have you ever tried to initialize an array? Many websites will tell you that this is not possible. In fact, if you try this you’ll get a compiler error:

class array {
public:
  bool vars[2];
  array() : vars[0](true), vars[1](true) {}
};

BUT, if all you want to do is zero-initialize the array then you’re in luck! Simply place parens after the array and the array will be zero-initialized. Try out the code below:

#include <iostream>

class arrayInit {
 public:
  bool vars[2];

  arrayInit() : vars() {}
};

class array {
 public:
  bool vars[2];
  array() {}
};

int main()
{
  arrayInit a;
  std::cout << "a.vars[0] = " << a.vars[0] << std::endl;
  std::cout << "a.vars[1] = " << a.vars[1] << std::endl;

  array b;
  std::cout << "b.vars[0] = " << b.vars[0] << std::endl;
  std::cout << "b.vars[1] = " << b.vars[1] << std::endl;
}

Using code like this in Visual Studio can generate warning C4351 because the behavior is different from previous versions of VC++. Here is the documentation from MSDN:

Compiler Warning (level 1) C4351

new behavior: elements of array ‘array’ will be default initialized

When an array is in a constructor’s member initialization list, the elements of the array will be default initialized. In previous versions of Visual C++, when an array was in a constructor’s member initialization list, the elements of the array may not have been default initialized in some cases.

If the array’s element type does not have a constructor, the elements of the array will be initialized with the corresponding zero representation for that type.

C4351 means that you should inspect your code. If you want the compiler’s previous behavior, remove the array from the constructor’s member initialization list.

If you want the new behavior, which is likely, because the array was explicitly added to the constructor’s member initialization list, use the warning pragma to disable the warning. The new behavior should be fine for most users.

One situation where the new behavior can result in unexpected behavior is when placement new is used to construct the object that has the array as a member, and the program depends on the contents that the memory (for the elements of the default initialized array) had before the call to placement new. In this case, the older compiler would have left the contents of memory unchanged, but the new behavior will cause default initialization of the array elements, overwriting the original contents in memory.

Digraphs and trigraphs in C++

15 June, 2010 § Leave a comment

This is a guest blog post by A.J. Orians.

In C++ you can program using digraphs and trigraphs. They are character substitutions you can make that may be easier to type depending on your keyboard layout. For instance instead of the following code:

int main()
{
   int array[3];
   return 0;
}

Using digraphs and trigraphs it can be written as the following:

int main()
??<
   int array<:3:>;
   return 0;
??>

However Visual Studio will not compile using digraphs and trigraphs. But it is still important to know about them because you could be creating cross-platform code that may fail and it may not be easy to understand why. Take the following piece of code:

#include <vector>
using namespace std;

class A{};

int main()
{
   vector<::A> vect;
   return 0;
}

Under g++ it will fail to compile with the following error:

main.cpp: In function int main():
main.cpp:8: error: <:: cannot begin a template-argument list
main.cpp:8: note: <: is an alternate spelling for [. Insert whitespace between < and ::
main.cpp:8: note: (if you use -fpermissive G++ will accept your code)

The reason why is vect; which is an error. To fix this error just put a space between the < and the ::A.

Finding how a header file gets included

6 May, 2010 § 2 Comments

Have you ever had a header file generate warnings that is not explicitly part of your Visual Studio solution?

Recently I’ve been working on fixing static analysis warnings reported by Microsoft’s PREfast static analysis tool for C++. I ran in to an issue though with some of the Microsoft Windows SDK v6.0 headers. One file, aptly named `strsafe.h`, can be the cause for tons of warnings in a build.

I looked around and found that the Windows SDK team is fully aware of the problem. They recommend wrapping the include for strsafe.h with pragmas, like so:

#include <CodeAnalysis/warnings.h>
#pragma warning(push)
#pragma warning(disable: ALL_CODE_ANALYSIS_WARNINGS)
#include <strsafe.h>
#pragma warning(pop)

So the first thing I did was to search through my code and find out who what included strsafe.h. But it turns out that no file explicitly included it. I figured that it must get included from another include file.

To find out what files are included in your build, you can turn on /showIncludes through the Project Properties ➨ Configuration Properties ➨ C/C++ ➨ Advanced ➨ Show Includes

/showIncludes prints out a tree of all of the files that get included in when the project is built. Using this, I was able to find which SDK files we included that ended up including strsafe.h.

This process took me about a half hour in total from turning the compiler flag on, performing a rebuild, narrowing down the includes, and wrapping them with pragmas. I still got a nasty taste in my mouth for suppressing the warnings, but getting rid of them cut out a lot of noise surrounding actual warnings that are more pressing.

C++0x support in VC10 (VS2010)

15 February, 2010 § 4 Comments

I’ve been using Visual Studio 2010 since the Beta 2 release and just a couple days ago installed the Release Candidate.

VC10 has support for some of the features of C++0x and I wanted to get a head start on playing with the features so that when we switch production environments at work I will be ready to start taking advantage.

While getting to know VC10 and C++0x, I’ve noticed a couple low-severity issues that I wanted to point out:

Lambda Functions

Lambda functions allow you to create an inline functor. They don’t supply any new capabilities of the language, but they cut out a lot of noise. Here is an example usage:

std::vector<int> numbers;

numbers.push_back(1);
numbers.push_back(2);

std::for_each(numbers.begin(), numbers.end(), [](int number){ std::cout << number << std::endl; });

Pre-C++0x, you would have had to write this:

struct Functor {
  void operator()(int number) {
    std::cout << number << std::endl;
  }
};

std::vector<int> numbers;
numbers.push_back(1);
numbers.push_back(2);

std::for_each(numbers.begin(), numbers.end(), Functor());

The thing that I have noticed is that if you use using-declarations throughout your code, not all of them get captured from inside of the lambda. For example, this does not work:


void exampleFunction( const std::vector<int>& numbers ) {
using std::cout;
using std::endl;

std::for_each(numbers.begin(), numbers.end(), [](int number){ cout << number << endl; });

For some reason, endl is not captured, and the VC10 compiler throws an error. However, either of these do work:


void exampleFunction2( const std::vector<int>& numbers) {
  std::for_each(numbers.begin(), numbers.end(), [](int number){ std::cout << number << std::endl; });
}

// or

using namespace std;
void exampleFunction3( const std::vector<int>& numbers) {
  std::for_each(numbers.begin(), numbers.end(), [](int number){ cout << number << endl; });
}

Also, if the lambda-return-type-clause is not specified, then implicit type conversion warnings do not get generated:


std::deque<int> integers;
std::transform(numbers.begin(), numbers.end(), std::front_inserter(integers), [](int number){
  return number > 0 ? number / 2.0 : number * 2;  // no warning here
});

std::transform(numbers.begin(), numbers.end(), std::front_inserter(integers), [](int number) -> int {
  return number > 0 ? number / 2.0 : number * 2;  // warning C4244: 'return' : conversion from 'double' to 'int', possible loss of data
});

It doesn’t seem like the type inference is doing a great job with the compiler warning here. I would recommend explicitly specifying the lambda-return-type-clause to get full type checking by the compiler.

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