另一个讨论的结论是:

内联函数有什么缺点吗?

显然，使用内联函数并没有什么错。

但值得注意的是以下几点!

Overuse of inlining can actually make programs slower. Depending on a function's size, inlining it can cause the code size to increase or decrease. Inlining a very small accessor function will usually decrease code size while inlining a very large function can dramatically increase code size. On modern processors smaller code usually runs faster due to better use of the instruction cache. - Google Guidelines The speed benefits of inline functions tend to diminish as the function grows in size. At some point the overhead of the function call becomes small compared to the execution of the function body, and the benefit is lost - Source There are few situations where an inline function may not work: For a function returning values; if a return statement exists. For a function not returning any values; if a loop, switch or goto statement exists. If a function is recursive. -Source The __inline keyword causes a function to be inlined only if you specify the optimize option. If optimize is specified, whether or not __inline is honored depends on the setting of the inline optimizer option. By default, the inline option is in effect whenever the optimizer is run. If you specify optimize , you must also specify the noinline option if you want the __inline keyword to be ignored. -Source

这并不完全是关于性能。c++和C都用于嵌入式编程，位于硬件之上。例如，如果您要编写中断处理程序，则需要确保代码可以立即执行，而不会交换额外的寄存器和/或内存页。这就是内联派上用场的时候。好的编译器在需要速度时自己做一些“内联”，但“内联”迫使它们这样做。

另一个讨论的结论是:

内联函数有什么缺点吗?

显然，使用内联函数并没有什么错。

但值得注意的是以下几点!

Overuse of inlining can actually make programs slower. Depending on a function's size, inlining it can cause the code size to increase or decrease. Inlining a very small accessor function will usually decrease code size while inlining a very large function can dramatically increase code size. On modern processors smaller code usually runs faster due to better use of the instruction cache. - Google Guidelines The speed benefits of inline functions tend to diminish as the function grows in size. At some point the overhead of the function call becomes small compared to the execution of the function body, and the benefit is lost - Source There are few situations where an inline function may not work: For a function returning values; if a return statement exists. For a function not returning any values; if a loop, switch or goto statement exists. If a function is recursive. -Source The __inline keyword causes a function to be inlined only if you specify the optimize option. If optimize is specified, whether or not __inline is honored depends on the setting of the inline optimizer option. By default, the inline option is in effect whenever the optimizer is run. If you specify optimize , you must also specify the noinline option if you want the __inline keyword to be ignored. -Source

内联函数是编译器使用的优化技术。可以简单地在函数原型前加上inline关键字来使函数内联。内联函数指示编译器在代码中使用函数的任何地方插入完整的函数体。

优点:-

It does not require function calling overhead. It also save overhead of variables push/pop on the stack, while function calling. It also save overhead of return call from a function. It increases locality of reference by utilizing instruction cache. After in-lining compiler can also apply intra-procedural optimization if specified. This is the most important one, in this way compiler can now focus on dead code elimination, can give more stress on branch prediction, induction variable elimination etc..

要了解更多信息，可以点击这个链接 http://tajendrasengar.blogspot.com/2010/03/what-is-inline-function-in-cc.html

在优化过程中，许多编译器会内联函数，即使你没有标记它们。如果你知道一些编译器不知道的东西，你通常只需要将函数标记为内联，因为它自己通常可以做出正确的决定。

Generally speaking, these days with any modern compiler worrying about inlining anything is pretty much a waste of time. The compiler should actually optimize all of these considerations for you through its own analysis of the code and your specification of the optimization flags passed to the compiler. If you care about speed, tell the compiler to optimize for speed. If you care about space, tell the compiler to optimize for space. As another answer alluded to, a decent compiler will even inline automatically if it really makes sense.

另外，正如其他人所说，使用内联并不能保证任何东西都是内联的。如果你想要保证它，你必须定义一个宏而不是一个内联函数来实现它。

何时内联和/或定义宏强制包含?-只有当你对关键代码段的速度有了证明和必要的提高，并且知道这对应用程序的整体性能有影响时。