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有感于講C語(yǔ)言的DLL文件的文章很少，自己查了半天，寫(xiě)了這么個(gè)非常簡(jiǎn)單的教程。自己也是摸C語(yǔ)言不久，依然感覺(jué)處于編程苦手的階段。 1）為什么使用DLL文件 C語(yǔ)言復(fù)用代碼有很多的形式，利用動(dòng)態(tài)鏈接庫(kù)（DLL）來(lái)復(fù)用代碼也是一種很有效的做法。使用DLL相比利用靜態(tài)庫(kù)來(lái)復(fù)用代碼有幾點(diǎn)不同： a. 可以不用寫(xiě) header File，但是在編譯過(guò)程中需要在編譯器里把文件鏈接起來(lái)； b. 更加靈活，可以只改動(dòng)和編譯DLL文件的內(nèi)容，而不用對(duì)程序其他部分進(jìn)行修改； c. 利用DLL文件可以方便地與其他語(yǔ)言進(jìn)行鏈接（比如Python）。 2）創(chuàng)建DLL及C語(yǔ)言調(diào)用程序 目前看來(lái)，創(chuàng)建 DLL 文件和創(chuàng)建普通c語(yǔ)言文件沒(méi)有什么不同。創(chuàng)建 C++ 的 DLL 文件要更復(fù)雜一些，C則相對(duì)簡(jiǎn)單。照著 C 代碼的格式寫(xiě)一個(gè)文件（注：C++ 似乎會(huì)不同，微軟就有教程，可以查閱VS的幫助文檔）。 以下是一個(gè)實(shí)例，文件名為 TestDll.c //TestDll.c?

#include <</font>stdio.h>

int hello()
{
????printf("Hello from DLL\n");
}

int SumNumbers(int a, int b)
{
????intc;
????c=a+b;
????returnc;
} 然后寫(xiě)一個(gè)主程序來(lái)調(diào)用，文件名為 UseTestDll.c //UseTestDLL.c?

#include <</font>stdio.h>

int main()
{
????hello();
????hello();
????inta=2,b=3;
????intc;
????c=SumNumbers(a,b);
????printf("c= %d.\n",c);
} ? 搞定。 3）編譯及運(yùn)行 測(cè)試使用的是 MinGW 下的 gcc 編譯器。 a. 編譯 DLL 文件 先將 c 文件編譯成 o 文件，然后再講 o 文件編譯成為 DLL 文件，在 cmd 里面代碼如下： gcc -c TestDLL.c
gcc -shared -o TestDll.dll TestDll.o 這樣就得到了 TestDll.dll 文件，如果文件多的話可以寫(xiě)個(gè)Batch文件來(lái)搞定。 b. 編譯使用文件 gcc -o UseTestDllUseTestDll.c -L./ -lTestDll 這樣就得到了 UseTestDll.exe 文件。UseTestDll.exe 和 TestDll.dll形成了程序的兩個(gè)部分，缺一不可。 運(yùn)行一下：

4）在Python中使用已有的Dll文件 DLL文件一樣可以在Python中使用。我們可以利用python自帶的ctypes模塊（python2.5后自帶，之前得自己再去下，不過(guò)現(xiàn)在也沒(méi)有人用2.5之前的了吧）。下面是一個(gè)示例文件，文件名為UseCDll.py from ctypesimport *

# Simple Test on c_int object
i=c_int(5)
print i
print i.value
i.value=10
print i.value

# Import Dll
TestDll=CDLL('TestDll.dll')

# Test Print Function
TestDll.hello()

# Test variable dilivery
a=c_int(4)
b=c_int(6)
c=TestDll.SumNumbers(a,b)
print c 函數(shù)說(shuō)明：

• c_int() 在python下創(chuàng)建c的int類(lèi)型對(duì)象，因?yàn)閜ython的數(shù)據(jù)類(lèi)型和c的數(shù)據(jù)類(lèi)型需要轉(zhuǎn)換
• CDLL() 讀入DLL文件，并將其轉(zhuǎn)化為一個(gè)對(duì)象，利用 對(duì)象.函數(shù) 的形式調(diào)用DLL里面的函數(shù)

運(yùn)行一下：

成功實(shí)現(xiàn)了在Python下使用DLL文件，這種方法可以減少代碼重復(fù)開(kāi)發(fā)，同時(shí)由于C的速度比Python大很多，還可以用這個(gè)方法對(duì)Python進(jìn)行加速。 5）APPENDIX 關(guān)于gcc編譯命令的一些說(shuō)明，來(lái)自gcc官方文檔。

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-shared Produce a shared object which can then be linked with otherobjects to form an executable. Not all systems support this option.For predictable results, you must also specify the same set ofoptions used for compilation (‘-fpic’, '-fPIC’, or modelsuboptions) when you specify this linker option.¹ 1 On some systems, ‘gcc -shared’ needs to build supplementarystub code for constructors to work. On multi-libbed systems, ‘gcc -shared’ must select the correctsupport libraries to link against. Failing to supply the correct flags may lead to subtle defects. Supplyingthem in cases where they are not necessary is innocuous

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-Ldir Add directory dir to the list of directories to besearched for ‘-l’.

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-o file Write output to file. This is the same as specifying file asthe second non-option argument to cpp. gcc has a differentinterpretation of a second non-option argument, so you must use‘-o’ to specify the output file.

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-c Compile or assemble the source files, but do not link. Thelinking stage simplyis not done. The ultimate output is in the formof an object file for each source file. By default, the object filename for a source file is made by replacing the suffix ‘.c’, ‘.i’,‘.s’, etc., with ‘.o’. Unrecognized input files, not requiring compilation orassembly, are ignored.

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-llibrary -l library Search the library named library when linking. (The secondalternative with the library as a separate argument is only forPOSIX compliance and is not recommended.) It makes a differencewhere in the command you write this option; the linker searches andprocesses libraries and object files in the order they arespecified. Thus, ‘foo.o -lz bar.o’ searches library ‘z’ after file‘foo.o’ but before ‘bar.o’. If ‘bar.o’ refers to functions in ‘z’, thosefunctions may not be loaded. The linker searches a standard list ofdirectories for the library, which is actually a file named‘liblibrary.a’. The linker then uses this file as if it had beenspecified precisely by name. The directories searched include several standard systemdirectories plus any that you specify with ‘-L’. Normally the files found this way are library files—archivefiles whose members are object files. The linker handles an archivefile by scanning through it for members which define symbols thathave so far been referenced but not defined. But if the file that is found is an ordinary object file, itis linked in the usual fashion. The only difference between usingan ‘-l’ option and specifying a file name is that ‘-l’ surroundslibrary with ‘lib’ and ‘.a’ and searches several directories.

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