blocks|key|4357326|text|因为当您使用#include+"Q2a.h"时，实质上是对内容进行文本替换，因此Q2a.cpp和Q2b.cpp最终都定义了一个名为MyFactorial()的函数。您需要使用inline，或者在某个源文件中定义该函数。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4357327|请注意，对于递归函数，使用inline不会有太大帮助！|4357328|entityMap^0|6|G|1T|D|2F|6|0|D|6|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|I|$]]

Because when you <code>#include "Q2a.h"</code>, you're essentially doing a text substitution of the contents, so both Q2a.cpp and Q2b.cpp end up defining a function called <code>MyFactorial()</code>. You either need to use <code>inline</code>, or define the function in one of the source files.

Note that using <code>inline</code> won't help very much with a recursive function!

blocks|key|2947450|text|在GCC将一个函数声明为inline时，它只会提示编译器内联该函数。但是，编译器仍然会生成一个非内联函数，您可以从不同的编译单元调用该函数。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2947451|在您的例子中，这些函数存在名称冲突。简单地说:内联并不意味着静态。|2947452|您要做的是将函数声明为static+inline|2947453|这将告诉编译器你想要你的函数内联，并且-如果编译器决定内联它-不需要相同函数的静态版本。如果编译器不能内联该函数，它将确保该函数是静态的，例如，该函数的名称是C文件的本地名称，并且在程序链接期间不会发生名称冲突。|2947454|提示：|BOLD|2947455|编译器有不同的行为。如果将来要在不同的平台上编译代码，请确保在宏中隐藏定义。|2947456|例如，我必须为GCC和Visual+Studio使用static+inline，为TI+Code+Composer+DSP/embedded+ARM编译器使用一个简单的_inline。后来的编译器不能理解普通的内联，因为它是非标准的，也不能理解静态_inline。|2947457|entityMap^0|C|6|0|0|B|D|0|0|0|3|0|0|Q|D|2C|7|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|11|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|12|8|@$9|13|A|14|B|N]]|D|@]|E|$]]|$1|O|3|P|5|6|7|15|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|T|$]]

With GCC declaring a function as <code>inline</code> will just hint the compiler to inline the function. However, the compiler will still generate a non-inline function that you can call from a different compilation unit. 

These functions had a name collision in your case. Simply said: inline doesn't imply static.

What you want to do is to declare the functions as <code>static inline</code> 

This will tell the compile that you want your function inline, and - if the compiler decides to inline it - no static version of the same function is required. It otoh the compiler can't inline the function it will make sure that the function is static, e.g. the name of the function is local to the C-file and no name collisions during linking of the program will occur.

Hint:

Compilers have different behaviour. If you want to compile the code on a different platform in the future make sure that you hide the definition in a macro. 

For example I have to use <code>static inline</code> for the GCC and Visual Studio and a simple <code>_inline</code> for the TI Code Composer DSP/embedded ARM compiler. The later compiler doesn't understand a plain inline because it is non-standard and won't understand static _inline either.

blocks|key|993375|text|当您声明一个函数inline时，您更改了应用于函数定义的规则。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|993376|非inline函数在程序中只能定义一次；相比之下，inline函数可以在多个翻译单元中定义，尽管定义必须相同，并且必须在使用它的每个翻译中定义该函数。|993377|通过删除inline，您正在删除以前的"one+definition+rule“中的豁免。|993378|entityMap^0|8|6|0|1|6|P|6|0|4|6|0^^$0|@$1|2|3|4|5|6|7|L|8|@$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|K|$]]

When you declare a function <code>inline</code> you change the rules that apply for the definitions of your function.

A non-<code>inline</code> function must only be defined once in a program; in contrast an <code>inline</code> function may be defined in multiple translation units, although the definitions must be identical and the function must be defined in every translation in which it is used.

By removing <code>inline</code>, you are removing the exemption from the "one definition rule" that you had previously.

i have this files: 

<pre><code>//Q2a.h
#ifndef Q2A_H
#define Q2A_H

inline int MyFactorial(int a)
{
if (a &lt; 2)
 return 1;
return a*MyFactorial(a-1);
}

int NumPermutations(int b);
#endif

//Q2a.cpp
#include "Q2a.h"

int NumPermutations(int b)
{
 return MyFactorial(b);
}

and file with the main- Q2b.cpp
</code></pre>

i notice that the compiler usually ignore the inline decleration when there are recursive functions .
but my question is why if i remove the inline declaration, i can do:

<pre><code>g++ -Wall -g -c Q2a.cpp -o Q2a.o
g++ -Wall -g -c Q2b.cpp -o Q2b.o
</code></pre>

those are fine, but in the linkage stage:

<pre><code>g++ -Wall -g -c Q2a.o Q2b.o -o Q2
</code></pre>

i get an error: multiple definition of `MyFactorial(int)

recursive inline function

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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我有这些文件：//Q2a.h#ifndef Q2A_H#define Q2A_Hinline int MyFactorial(int a){if (a < 2) return 1;return a*MyFactorial(a-1);}int NumPermutations(int b);#endif//Q2a.c...

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