blocks|key|2706922|text|正如您所说的，在.cpp中而不是在.h中定义方法可以提高性能和加快编译时间。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2706923|注意，这两个属性(性能和加速比)都应用于编译时间。它不会提高运行时的性能。|2706924|关于为什么它提高了编译时间的性能，这是因为该方法仅在定义它的.cpp中被解析和编译，而如果它是在.h中定义的，则在包含头的所有.cpp中进行解析和编译，从而降低了总的编译速度1。|2706925|2706926|1在这篇博文中，我们将对此作进一步的详细解释：http://gameangst.com/?p=224|2706927|entityMap|0|LINK|mutability|MUTABLE|url|http://gameangst.com/?p=224^0|8|4|H|2|0|0|U|4|1C|2|1R|4|0|0|N|R|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|17|8|@]|D|@]|E|$]]|$1|K|3|L|5|6|7|18|8|@]|D|@$9|19|A|1A|1|1B]]|E|$]]|$1|M|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

As you said, defining the method in the <code>.cpp</code> instead of in the <code>.h</code> improves performance and speedup of compilation time.

Note that both attributes (performance and speedup) are applied to compilation time. It does not improve performance at runtime.

About why it improves performance of compilation time, it is because the method is only parsed and compiled in just the <code>.cpp</code> where it is defined, while if it is defined in the <code>.h</code> it is parsed and compiled in all the <code>.cpp</code>s where the header is included, thus reducing the total compilation speed [1]

<hr>

[1] In this blog post, it is explained further and with more detail:
<a href="http://gameangst.com/?p=224" rel="nofollow noreferrer">http://gameangst.com/?p=224</a>

blocks|key|2706951|text|如果函数是在类内定义的，编译器允许将其内联，而不是调用它(基本上将代码复制到调用的位置)。这可以提高运行时性能。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2706952|但是，内联函数也会导致编译每个，其中包含类的头文件将重新编译精确的函数定义，这可能会使构建过程更长。|2706953|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

If a function is defined inline in a class, the compiler is allowed to put it inline instead of calling it (basically copies the code into the location of the call). That can improve run-time performance.

But also, inline functions will cause the compilation of each <a href="https://en.wikipedia.org/wiki/Translation_unit_(programming)" rel="nofollow noreferrer">translation unit</a> where the header file containing the class to recompile that exact function definition which could make the build-process longer.

blocks|key|2731942|text|只要将函数定义编译成单个二进制，函数定义的位置就不会对代码性能产生影响。请注意，即使函数没有在头文件中定义，即使它们是在头文件中定义的，也可能是内联的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2731943|根据项目组织的不同，将定义放入头文件而不是在.cpp文件中可能会极大地改善构建时间或使其变得更糟。对于最快的构建，将定义放入头文件是必须的。|2731944|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Location of function definition has no impact on code performance as long as it is compiled into a single binary. Note that functions may be inlined even if they are not defined in header files and may be not inlined even if they are defined in header files.

Depending on project organization putting definitions into header files rather than in .cpp files may greatly improve build times or make them worse. For fastest builds putting definitions into header files is mandatory.

blocks|key|1779797|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1779798|+...将提高性能和加速编译时间。|blockquote|1779799|1779800|1779801|这本书第一部分写错了。它不能提高程序外部定义函数的(运行时)性能。事实上，如果不是因为链接时间优化，它会产生相反的效果，因为它可能会阻止内联扩展。|1779802|后一种说法不那么可疑，尽管真理并不那么简单。拥有多个翻译单元通常会从零开始减缓项目的编译时间。然而，能够只编译已更改的翻译单位可以大大减少增量变化的编译时间，当这些翻译单位是小的。|1779803|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|-4|4|5|6|L|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|M|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|N|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|O|7|@]|8|@]|9|$]]|$1|F|3|G|4|5|6|P|7|@]|8|@]|9|$]]|$1|H|3|I|4|5|6|Q|7|@]|8|@]|9|$]]|$1|J|3|-4|4|5|6|R|7|@]|8|@]|9|$]]]|K|$]]

<blockquote>
 ... will improves performance and speedup compilation time
</blockquote>

The book is wrong on the first part. It does not improve (runtime) performance of a program to define functions externally. In fact, if it wasn't for link time optimisation, it would have the opposite effect due to potentially preventing inline expansion.

The latter claim is not as dubious, although truth is not that simple. Having multiple translation units generally slows down the compilation time of the project from scratch. However, being able to compile only the translation units that have been changed can significantly reduce the compilation time of incremental changes when those translation units are small.

blocks|key|2707080|text|当您将方法定义放入.cpp文件中时，它只编译一次，其他.cpp文件中该方法的每个调用都将链接到该方法的单个编译版本。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2707081|如果将方法定义放入头文件中，就好像将其复制粘贴到头文件中的每个.cpp文件中一样，并且必须在每个.cpp文件编译中分别编译，这当然比编译一次要花费更多的时间。|2707082|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

When you put the method definition into a .cpp file, it gets compiled once and every call of this method in other .cpp files will get linked to this single compiled version of the method.

If you put the method definition into header file, it's as if you copy pasted it into every .cpp file the header is included in, and it has to be compiled in each .cpp file compilation separately, which of course takes more time than compiling it once.

I read in a book that defining the method (of a class) in a <code>.cpp</code> file rather than defining it inside the class in declaration (<code>.h</code> file) will reduce memory usage and speed up compilation time.

<blockquote>
 Moving member function definitions from class definition to a separate .cpp file generally speeds up compilation times and reduces memory usage
</blockquote>

I tried to implement it in C++ code, but the execution time varies at every time, so I am unable to examine it clearly. Can anyone help me to understand this concept?

how the performance of the code gets increased while defining the method in .cpp file rather than defining it in the .h file in c++?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我在一本书中读到，在.cpp文件中定义(类的)方法，而不是在类中声明(.h文件)中定义它，将减少内存使用并加快编译时间。将成员函数定义从类定义移动到单独的.cpp文件，通常会加快编译时间并减少内存使用。我试图在C++代码中实现它，但是每次执行时间不同，所以我无法清楚地检查它。有人能帮我理解这个概念吗？

问在.cpp文件中定义方法而不是在c++中的.h文件中定义方法时，如何提高代码的性能？
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问在.cpp文件中定义方法而不是在c++中的.h文件中定义方法时，如何提高代码的性能？EN