With the Android NDK Google lets us write C/C++ code for Android. I don’t like writing C/C++ code because it’s error-prone but sometimes there’s no other way.
Unfortunately (this is the “I don’t like this” part), debugging Android C/C++ code is terribly difficult. If you don’t have a week to get the debugging toolchain working, and if you only need some quick and temporary solution, logging may be an alternative.
This article is the second part of the subprojects mini series. The first part was about creating a DLL project. This part will show how to use a DLL library project in another project.
Referencing a library in C++ (or, more specific, with Visual C++) is somewhat cumbersome – or should I say, used to be somewhat cumbersome. Fortunately, with the release of Visual C++ 2010 this has been greatly simplified. This article first shows the old way and then describes the new (simple) way.
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In this part of the “Projects in Visual C++ 2010” mini series another important aspect of C++ programming is explain: precompiled headers. Precompiled headers (or precompiled header files) in many cases significantly reduce the time needed to compile a project.
Here at work I have a C++ project with about 50 .cpp files in it. The project uses the Qt library and all files only include the absolute minimum of header files required. Without precompiled headers, compiling the project takes about 56 seconds. With precompiled headers, the compile time goes down to about 7 seconds. That’s eight times faster.
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The last few days I’ve been hunting a bug in a C++ project I’ve been working on. This hunt again showed me how easily you can break C++ programs by accident (something that isn’t possibly in Java or C#). You need to completely understand the inner workings of C++ to avoid such pitfalls.
The whole problem was a result of me thinking that C++ references (&) are just pointers (*) that have some restrictions (e.g. they can’t be NULL). Wrong! What’s even worse: They’re sometimes just pointers with some restriction. This makes them work in some cases but fail in others.
Let me take you on my journey and you’ll hopefully avoid this (very subtle) mistake in your work.
During my time as a student at the University of Stuttgart we had to learn the programming language Ada. Back then I was swearing about the compiler error message because they were totally meaningless (at least to me).
I am currently working on a C++ project and I have to say that C++ isn’t an inch better than Ada. Consider the following code:
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#include <Windows.h> namespace Geometry { class Polyline { }; } using Geometry::Polyline; namespace OtherNS { Polyline* get() { return NULL; } } |
Trying to compile this code gives you the following error message (on Visual C++ 2010):
using_test.cpp(10): error C2143: syntax error : missing ';' before '*' using_test.cpp(10): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int using_test.cpp(10): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
What? Syntax error? And then you start looking where you missed a ;.
The problem, however, is completely different. It’s because there is a function called Polyline() defined somewhere in Windows.h and now the compiler tries to use this function as return type instead of the class Polyline (but doesn’t say anything about that). <irony>This, of course, becomes totally clear just by reading this extremely meaningful error message.</irony> *sigh*
GCC isn’t better here (in case you were blindly blaming Microsoft for writing bad error messages):
error: ‘Polyline’ does not name a type
By the way, the problem can be solved by placing the using statement inside the OtherNS namespace.