Menu
Lets say you have simple template function (not class member for the sake of simplicity) with type specific specialization in the same .h file...
template <class TYPE>
void some_function(TYPE& val)
{
// some generic implementation
}
template <>
inline void some_function<int>(int& val)
{
// some int specific implementation
}
Unless you explicitly direct you compiler to inline the specialization (inline keyword) you will get linking error if .h file is included more than once (at least I do in Visual C++ 2008).
We all know that inline is just a suggestion to the compiler, which it can ignore. In this particular case is compiler allowed to ignore this suggestion and let linker to fail?
383
Remember, inlining is only a request to the compiler, not a command. Compiler can ignore the request for inlining. Compiler may not perform inlining in such circumstances like: If a function contains a loop.
Yes, you need the inline specifier there. The ODR (one-definition rule) states that there must be exactly one definition of a variable, function, class, enum or template.
When we should avoid the use of inline? We should not use functions that are I/O bound as inline functions. When large code is used in some function, then we should avoid the inline. When recursion is used, inline function may not work properly.
Automatic function inlining and static functions At -O2 and -O3 levels of optimization, or when --autoinline is specified, the compiler can automatically inline functions if it is practical and possible to do so, even if the functions are not declared as __inline or inline .
If you don't use inline, then the same function gets compiled with extern linkage into multiple .obj files, which causes the linker to throw a duplicate symbol error.
This is independent of whether the compiler actually compiles your function inline, since it could treat it the same as a static function and make each implementation private to each compilation unit. However, you can't use static for this purpose since it means something else on member functions, so inline is your only choice.
130
You are misunderstanding the meaning of the often-mentioned "ignore inline" possibility.
No compiler is ever allowed to ignore the inline specifier used in function declaration and the consequences this specifier has with respect to One Definition Rule (ODR).
When someone says that compiler are allowed to "ignore inline", it only means that compilers are not required to actually inline the calls to the function in question. To "ignore inline" means to generate an ordinary (non-inlined) function call to an inline function.
In any case, even if the compiler decided to always generate ordinary calls to an inline function (i.e. to always "ignore inline"), it is still required to treat the function as inline for the purposes of ODR. How the compiler is going to do it is the problem of the compiler. You are not supposed to worry about it.
In your original example you should not not get any linker errors.
30
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
