Pragma

[Imposter]

How can i use a pragma directive in order to show warning by compiler when a variable is declared twice.. That is

class a
{
int b;
void f()
{
int b;
}
};

although it is getting compiled without warning.

[weaknessforcats]

Your variable is not defined twice.

There are two variables. They have the same name which is OK because the scope is different.

[Banfa]

pragmas are entirely compiler dependent, you only have what your compiler provides.

However in general no compiler provides a way to add warnings. If the compiler is able to do it it will already be a part of the compiler.

As weaknessforcats says your problem is that you have defined two variables at different scopes but because they have the same name the one in a::f hides the member declaration in a.

Static analysis tools, such as PCLint will pick up this sort of error.