Tag Archives: c++

Reasons against advising beginners to use Dev-C++ in 2011

You may be tempted to recommend Dev-C++ to a beginner, or you may be a beginner tempted to use it.

Stop.

It’s 2011. Dev-C++ is not in development since 2005. Its latest version is a beta, and as you code, its beta status will be felt. Here is a short list of why a beginner should not use Dev-C++, and why he will not miss it after no longer being a beginner. Of course, this is also a list of reasons why competent and advanced coders should not use it. (Update March 28 2012: Here’s an additional opinion from way back in 2008.)
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Testing for presence of Apple platform in C/C++/ObjC code

Are we running on an Apple platform?
#ifdef __APPLE__
#endif
Prerequisite for other tests
#ifdef __APPLE__
// let Apple define 
// various TARGET_OS_ 
// constants
#include  
#else
// not on Apple platform
#define TARGET_OS_MAC 0
#define TARGET_OS_IPHONE 0
#endif
Are we running on Mac OS X?
#if TARGET_OS_MAC && !TARGET_OS_IPHONE
….
#endif
Are we running on an iOS device?
#if TARGET_OS_IPHONE
….
#endif
// updated on Oct13 2010, previous method was flawed. sorry everyone!

iPhone development: Bits/c++config.h: No such file or directory

Developing for iPhone with some C++ code? Suddenly getting this error after installing a beta SDK?

/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.2.sdk/usr/include/c++/4.2.1/bits/stl_algobase.h:65:0 Bits/c++config.h: No such file or directory in /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.2.sdk/usr/include/c++/4.2.1/bits/stl_algobase.h

Note the bolded folder. Change into it and make a symlink from arm-apple-darwin9 to arm-apple-darwin10. Please note that Apple has fixed this already at one upgrade of beta SDK (I had this error before too, but I still didn’t get 4.0 beta 2 so I didn’t check) so it’s reasonable to assume they will do this again.

cd Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.2.sdk/usr/include/c++/4.2.1/
ln -s arm-apple-darwin9 arm-apple-darwin10

PS I don’t think posting this violates any NDA. Especially since origin for this solution is also public.

Fixing “warning: missing sentinel in function call”

I got it for the folowing line:

execl("/bin/sh", "sh", "-c", sessioncommand.c_str(), 0);

Quite easy to fix:

execl("/bin/sh", "sh", "-c", sessioncommand.c_str(), (char*)0);

—————————————–

Alright. Since I’m getting “lots” of hits on this, let’s see if we can improve this post. (June 28th 2010, more examples added July 22nd 2010, style but not content updated April 19 2014)

Generally, you’re missing a sentinel if you don’t add a “NULL” in C/C++, or a “nil” in Objective-C. In above example in C, I presume the compiler did not notice the zero (a valid sentinel) and threw a warning. That’s what this post was mostly about.

However, it could also happen if you really did forget to add the sentinel. What is the purpose of this “sentinel”? When iterating through a varlist**, the function needs to know where to stop. In printf() and scanf(), the format string specifies this number of arguments. Functions could also accept the number of arguments as one of the arguments. Third option is this — specifying a sentinel, such as NULL or nil, as something that will stop further iteration.

Examples of sentinels in C:

execl("/bin/sh", "sh", "-c", sessioncommand.c_str(), NULL);

and in Objective-C:

NSArray *names = [NSArray arrayWithObjects: @"Ivan", @"Ana", @"Marko", @"Petar", nil];

** Iterating through a varlist – which is how you iterate through arguments in variadic functions, those with variable number of arguments

close() of listening socket from another thread

Just a warning.

Calling close() on listening socket in another thread will NOT prevent another connection from being made. Instead, you must call shutdown(). This should abort existing select() calls (probably accept() too, but I didn’t try).

Guess how I found out 🙂

Great new GCC option – Effective-C++ Warnings

Did you know about -Weffc++ in GCC? Neither did I, until I upgraded to new Code::Blocks from Jens’ unofficial Debian repository for Code::Blocks.

Here’s a few sample warnings, with sample lines and commentary:

  • /home/ivucica/Development/project/src/types.h|12|warning: ‘operator=’ should return a reference to ‘*this’|

Sample:
Position &operator=(const Position& other) { x=other.x; y=other.y; z=other.z; return *this;}

What’s the big deal here? By leaving out the ampersand in this operator overloading, I accidentally returned a copy of entire Position class. (On the other hand, I had no reason to actually overload this operator so perhaps real fix is to erase entire line. Still…)

  • /home/ivucica/Development/project/src/mat.h|10|warning: ‘class Mat’ has pointer data members|
    /home/ivucica/Development/project/src/mat.h|10|warning: but does not override ‘Mat(const Mat&)’|
    /home/ivucica/Development/project/src/mat.h|10|warning: or ‘operator=(const Mat&)’|

No sample needed.

What’s the problem here? Well, we have a Mat class containing pointer. So what happens when someone does this: Mat x = y; or this: Mat x(y);? We have another instance of a class with copies of all the data, except the data pointed to by the pointer. Instead the pointer itself gets copied.

So if we keep a C-style string in there, we’re not really copying the string … we’re copying the pointer to it, and modifying the string in the new instance still modifies the string in the original ocpy.

While not applicable everywhere, still a good and useful warning.

  • /home/ivucica/Development/project/src/obj.h||In constructor ‘Obj::Obj()’:|
    /home/ivucica/Development/project/src/obj.h|15|warning: ‘Obj::m_radius’ should be initialized in the member initialization list|

Simple. Instead of initializing (or forgetting to initialize, or intentionally doing so) a variable in the constructor:
Obj() {m_classname=”Obj”; m_usecount = 0; }
why not do it in a “safe” and readable way (and perhaps more optimal?)
Obj() : m_classname(“Obj”), m_usecount(0) { }

While these warnings are certainly not the Universal Elixir to cure all your troubles, they will certainly prove useful in furthering your 1337 skills.