I'm using g++ with the -Wunreachable-code and the -Wfatal-errors -Werror options enabled to compile a piece of code, but... when I use the standard string header I get an unreachable code error and I don't know why.
cc1plus: warnings being treated as errors
/usr/include/c++/4.4/bits/basic_string.h: In constructor ‘std::basic_string<_CharT, _Traits, _Alloc>::basic_string() [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]’:
/usr/include/c++/4.4/bits/basic_string.h:2147: error: will never be executed
compilation terminated due to -Wfatal-errors.
Is my code wrong? Is a bug in the header file? Is a false positive?
Why there is a statement that will never be executed?
I have searched the web but I haven't found an answer easily. If someone could help me I would be very pleased.
The optimiser may drop some of your code, in which case it'll tell you wtih -Wunreachable-code. But if you then tell the compiler to treat warnings as errors with -Wfatal-errors, then it'll treat the warning as an error and stop. http://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
"Warn if the compiler detects that code will never be executed.
This option is intended to warn when the compiler detects that at least a whole line of source code will never be executed, because some condition is never satisfied or because it is after a procedure that never returns.
It is possible for this option to produce a warning even though there are circumstances under which part of the affected line can be executed, so care should be taken when removing apparently-unreachable code.
For instance, when a function is inlined, a warning may mean that the line is unreachable in only one inlined copy of the function.
This option is not made part of -Wall because in a debugging version of a program there is often substantial code which checks correct functioning of the program and is, hopefully, unreachable because the program does work. Another common use of unreachable code is to provide behavior which is selectable at compile-time."
First of all thanks for your gentile answer.
I knew that -Werror (I made a mistake in my first post and I wrote -Wfatal-errors when it should say -Werror) converts warnings into errors (stopping the compiler). That is intentional to force me to fix any warning before continue coding.
What I didn't know was that the dropping was induced by the optimization process. (Thanks a lot for the clarification.)
But I would be interested in knowing how can avoid that dropping not in knowing how can avoid that warning.
If I would like to turn off that warning I could use: