c++ - Why am I getting no warning when writing = instead of ==? -

struggled during hours identify bug due invalid statement:

... assert( variable = -0.5 ); 

this should assert( variable == -0.5 );: developer typo.

i'm compiling visual studio 2015, , work on having "0-warning compilation".

how such bad , dangerous statement compile no warning being reported compiler? there no compiler option can enable avoid this?

edit: bool b = ( variable = -0.5 ) not produce compiler warning

assignments within conditional expressions warned against if using /w4 compilation level, see see this.

so tested using online msvc compiler (i don't have vs 2015 on pc) on code:

//microsoft (r) c/c++ optimizing compiler version 19.00.23506 x86  #include <iostream> #include <cassert> int main(){     int a;     if (a = 2){         std::cout << "hello, world!\n";     }     assert(a = 3); } 

and command line: source_file.cpp -o a.exe /ehsc /md /w4 /i c:\boost_1_60_0 /link /libpath:c:\boost_1_60_0\stage\lib , both lines warned:

warning(s): source_file.cpp(9) : warning c4706: assignment within conditional expression source_file.cpp(12) : warning c4706: assignment within conditional expression 

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apparently qt header qglobal.h disables warning using qt_warning_disable_msvc(4706) under configurations.