有感于讲C语言的DLL文件的文章很少,自己查了半天,写了这么个非常简单的教程。自己也是摸C语言不久,依然感觉处于编程苦手的阶段。
1)为什么使用DLL文件
C语言复用代码有很多的形式,利用动态链接库(DLL)来复用代码也是一种很有效的做法。使用DLL相比利用静态库来复用代码有几点不同:
a. 可以不用写 header File,但是在编译过程中需要在编译器里把文件链接起来;
b. 更加灵活,可以只改动和编译DLL文件的内容,而不用对程序其他部分进行修改;
c. 利用DLL文件可以方便地与其他语言进行链接(比如Python)。
2)创建DLL及C语言调用程序
目前看来,创建 DLL 文件和创建普通c语言文件没有什么不同。创建 C++ 的 DLL 文件要更复杂一些,C
则相对简单。照着 C 代码的格式写一个文件(注:C++ 似乎会不同,微软就有教程,可以查阅VS的帮助文档)。
以下是一个实例,文件名为 TestDll.c
//TestDll.c 然后写一个主程序来调用,文件名为 UseTestDll.c
//UseTestDLL.c 搞定。
3)编译及运行
测试使用的是 MinGW 下的 gcc 编译器。
a. 编译 DLL 文件
先将 c 文件编译成 o 文件,然后再讲 o 文件编译成为 DLL 文件,在 cmd 里面代码如下:
gcc -c TestDLL.c 这样就得到了 TestDll.dll 文件,如果文件多的话可以写个Batch文件来搞定。
b. 编译使用文件
gcc -o UseTestDll
UseTestDll.c -L./ -lTestDll 这样就得到了 UseTestDll.exe 文件。UseTestDll.exe 和 TestDll.dll
形成了程序的两个部分,缺一不可。
运行一下:
4)在Python中使用已有的Dll文件
DLL文件一样可以在Python中使用。我们可以利用python自带的ctypes模块(python2.5后自带,之前得自己再去下,不过现在也没有人用2.5之前的了吧)。下面是一个示例文件,文件名为UseCDll.py
from ctypes
import * 函数说明:
运行一下:
成功实现了在Python下使用DLL文件,这种方法可以减少代码重复开发,同时由于C的速度比Python大很多,还可以用这个方法对Python进行加速。
5)APPENDIX
关于gcc编译命令的一些说明,来自gcc官方文档。
-shared
Produce a shared object which can then be linked with other
objects to form an executable. Not all systems support this option.
For predictable results, you must also specify the same set of
options used for compilation (‘-fpic’, '-fPIC’, or model
suboptions) when you specify this linker option.1
-Ldir Add directory dir to the list of directories to be
searched for ‘-l’.
-o file Write output to file. This is the same as specifying file as
the second non-option argument to cpp. gcc has a different
interpretation of a second non-option argument, so you must use
‘-o’ to specify the output file.
-c Compile or assemble the source files, but do not link. The
linking stage simplyis not done. The ultimate output is in the form
of an object file for each source file. By default, the object file
name for a source file is made by replacing the suffix ‘.c’, ‘.i’,
‘.s’, etc., with ‘.o’.
Unrecognized input files, not requiring compilation or
assembly, are ignored.
-llibrary -l library
Search the library named library when linking. (The second
alternative with the library as a separate argument is only for
POSIX compliance and is not recommended.) It makes a difference
where in the command you write this option; the linker searches and
processes libraries and object files in the order they are
specified. 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’, those
functions may not be loaded. The linker searches a standard list of
directories for the library, which is actually a file named
‘liblibrary.a’. The linker then uses this file as if it had been
specified precisely by name.
The directories searched include several standard system
directories plus any that you specify with ‘-L’.
Normally the files found this way are library files—archive
files whose members are object files. The linker handles an archive
file by scanning through it for members which define symbols that
have so far been referenced but not defined.
But if the file that is found is an ordinary object file, it
is linked in the usual fashion. The only difference between using
an ‘-l’ option and specifying a file name is that ‘-l’ surrounds
library with ‘lib’ and ‘.a’ and searches several directories.
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