macros - How to use the #error directive - C++ -

i'm creating self initializing arrays class in c++ , i'm wondering how i'd throw error not exception if user try , allocate more 0x7fffffff bytes.

similar <array> where:

error c2148: total size of array must not exceed 0x7fffffff bytes

this code 1 of constructor i'm testing this:

    template<typename t>     array<t>::array(const size_t _size) : _size(_size), _content(nullptr){         #define __size__ _size         #if (__size__ > 0x7fffffff)              #error total size of array must not exceed 0x7fffffff bytes.         #endif         _content = new t[_size];         memset(_content, 0, (sizeof(_content) * _size));     } 

the way i'm creating array below:

array<int> foo(-1) //-1 of size_t = ((2^31)*2)-1 error should shown since ((2^31)*2)-1 > ((2^31)*2)-1 

size_t's max size ((2^31)*2)-1 , 0x7fffffff (2³¹)-1 issue error isn't executing i've never used #if macro before , need work...

any appreciated.

you can't use preprocessor variables. preprocessor separate step run before compilation, , has no idea variables used in source , run-time values.

for might want use assert:

assert(_size <= 0x7fffffff); 

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if pass negative value function expecting unsigned values should compiler warning, , if not should enable more warnings.