内联关键字与标题定义 [英] Inline keyword vs header definition

问题描述

在一个函数之前使用inline关键字和在头文件中声明整个函数有什么区别？

所以...

  int whatever（）{return 4; } 
  

vs

.h： / p>

  inline int whatever（）; 
  

.cpp：

  inline int myClass :: whatever（）
 {
 return 4; 
} 
  

这样做：

  inline int whatever（）{return 4; } 
  

解决方案

有几个方面：

语言

• 当函数标有 inline 关键字，那么它的定义应该在TU中可用或者程序是错误的。


• 在类定义中定义的任何函数隐式标记为 inline 。

<

• 模板函数（非完全专用）获得与 inline 个。
  

编译器行为 b

• 标记为 inline 的函数将在每个目标文件中作为弱符号发出，


• 而编译器实际上内联调用（即，在使用点复制/粘贴代码，而不是执行常规函数调用）。完全由编译器自行决定。关键字的存在可能或不会影响决策，但最好是一个提示。

链接器行为

• 弱符号合并在一起，在最终库中出现一次。一个好的链接器可以检查多个定义是否一致，但这不是必需的。

What's the difference between using the inline keyword before a function and just declaring the whole function in the header?

so...

int whatever() { return 4; }

vs

.h:

inline int whatever();

.cpp:

inline int myClass::whatever()
{
    return 4;
}

for that matter, what does this do:

inline int whatever() { return 4; }

解决方案

There are several facets:

Language

• When a function is marked with the inline keyword, then its definition should be available in the TU or the program is ill-formed.
• Any function defined right in the class definition is implicitly marked inline.
• A function marked inline (implicitly or explicitly) may be defined in several TUs (respecting the ODR), whereas it is not the case for regular functions.
• Template functions (not fully specialized) get the same treatment as inline ones.

Compiler behavior

• A function marked inline will be emitted as a weak symbol in each object file where it is necessary, this may increase their size (look up template bloat).
• Whereas the compiler actually inlines the call (ie, copy/paste the code at the point of use instead of performing a regular function call) is entirely at the compiler's discretion. The presence of the keyword may, or not, influence the decision but it is, at best, a hint.

Linker behavior

• Weak symbols are merged together to have a single occurrence in the final library. A good linker could check that the multiple definitions concur but this is not required.

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