AMDG Patrick Horgan wrote:
Herb Sutter and Andrei Alexandrescu (who is following this discussion on boost) were kind enough to give me permission to quote their item 1 from C++ Coding Standards (note that I screen scraped this from [1]www.artima.com who also had their permission to post) You might consider buying a copy, it's a wonderful book;) :
Indeed. I've read it.
1. Compile cleanly at high warning levels.
Summary
Take warnings to heart: Use your compiler's highest warning level. Require clean (warning-free) builds. Understand all warnings. Eliminate warnings by changing your code, not by reducing the warning level.
Discussion
Your compiler is your friend. If it issues a warning for a certain construct, often there's a potential problem in your code.
Successful builds should be silent (warning-free). If they aren't, you'll quickly get into the habit of skimming the output, and you will miss real problems. (See Item 2.)
To get rid of a warning: a) understand it; and then b) rephrase your code to eliminate the warning and make it clearer to both humans and compilers that the code does what you intended.
Do this even when the program seemed to run correctly in the first place. Do this even when you are positive that the warning is benign. Even benign warnings can obscure later warnings pointing to real dangers.
Examples
Example 1: A third-party header file. A library header file that you cannot change could contain a construct that causes (probably benign) warnings. Then wrap the file with your own version that #includes the original header and selectively turns off the noisy warnings for that scope only, and then #include your wrapper throughout the rest of your project. Example (note that the warning control syntax will vary from compiler to compiler): // File: myproj/my_lambda.h -- wraps Boost's lambda.hpp // Always include this file; don't use lambda.hpp directly. // NOTE: Our build now automatically checks "grep lambda.hpp <srcfile>". // Boost.Lambda produces noisy compiler warnings that we know are innocuous. // When they fix it we'll remove the pragmas below, but this header will still exist. // #pragma warning(push) // disable for this header only #pragma warning(disable:4512) #pragma warning(disable:4180) #include <boost/lambda/lambda.hpp> #pragma warning(pop) // restore original warning level
This works great for suppressing warnings on msvc, but gcc says: test.cpp:1: warning: ignoring #pragma warning test.cpp:2: warning: ignoring #pragma warning test.cpp:3: warning: ignoring #pragma warning test.cpp:5: warning: ignoring #pragma warning
<snip>
Exceptions
Sometimes, a compiler may emit a tedious or even spurious warning (i.e., one that is mere noise) but offer no way to turn it off, and it might be infeasible or unproductive busywork to rephrase the code to silence the warning. In these rare cases, as a team decision, avoid tediously working around a warning that is merely tedious: Disable that specific warning only, disable it as locally as possible, and write a clear comment documenting why it was necessary.
IMHO, this really underestimates the number of spurious warnings that compilers are liable to generate if given half a chance. The issues for a library like Boost are somewhat different from what an application needs to deal with. First of all, warnings in headers don't just affect us, they affect all users of the library. In addition, we have no control over what warnings are enabled. We have to be able to deal with whatever users throw at us. Further, Boost has to run on many different compilers. Compiling with zero warnings on all compilers is simply infeasible. If we just wanted to make sure that silly errors are caught, it would be much more effective for each library developer to pick his favorite compiler and make sure that his code compiles cleanly with a reasonable warning level. Note that "reasonable" does not mean all possible warnings (Sutter and Alexandrescu not withstanding). There are some warnings that are always noise or are nonsense in the context of Boost. MSVC's C4512, tends to generate a large amount of noise and has only helped my find a bug once (I don't give much credit to it for this. I already knew the bug existed. It only helped because it happened to generate a template instantiation backtrace at exactly the right point). Another example is warnings that are designed for a specific programming paradigm. -Weffc++ is not appropriate with Boost, and the warnings that it generates can be impossible for us to suppress because they can occur in user code. In Christ, Steven Watanabe