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python调用C和C++接口动态库
python调用C接口
编写c接口代码
//capi.c
#include <stdio.h>
#include <stdlib.h>
char* foo(char* in)
{
printf("foo function input: %s\n", in);
return "OK";
}
char* exam(char *in)
{
printf("exam function input: %s\n",in);
return "OK";
}
编译c接口代码:
# gcc -o libcapi.so -shared -fPIC capi.c
编译后在本地目录下生成libcapi.so为C接口代码的动态库 编辑python代码
#pycall.py
import ctypes
libcapi = ctypes.cdll.LoadLibrary("./libcapi.so")
libcapi.foo("good")
libcapi.exam("good")
print "success!"
调用Python测试代码
# python pycall.py
foo function input: good
exam function input: good
success!
测试成功!
python调用C++接口
编辑C++接口代码
//cppapi.cpp
#include <iostream>
std::string foo(std::string in)
{
std::cout << "foo function input: " << in << std::endl;
return "OK";
}
char* exam(char *in)
{
std::cout << "exam function input: " << in << std::endl;
return (char*)"OK";
}
编译C++接口代码
# g++ -o libcppapi.so -shared -fPIC cppapi.cpp
编写python测试脚步
#pycall.py
import ctypes
libcppapi = ctypes.cdll.LoadLibrary("./libcppapi.so")
libcppapi.foo("good")
libcppapi.exam("good")
print "success!"
执行脚步测试:
# python pycall.py
Traceback (most recent call last):
File "pycall.py", line 5, in <module>
libcppapi.foo("good")
File "/usr/lib/python2.7/ctypes/__init__.py", line 378, in __getattr__
func = self.__getitem__(name)
File "/usr/lib/python2.7/ctypes/__init__.py", line 383, in __getitem__
func = self._FuncPtr((name_or_ordinal, self))
AttributeError: ./libcppapi.so: undefined symbol: foo
c++动态库中找不到foo方法,是因为c和c++的函数签名不一致，因为c++支持重载，所以按c++的方式是找不到同名的c函数的,先查看C接口libcapi.so动态库符号表
# nm -D libcapi.so
0000000000201038 B __bss_start
w __cxa_finalize
0000000000201038 D _edata
0000000000201040 B _end
000000000000072d T exam
000000000000075c T _fini
0000000000000700 T foo
w __gmon_start__
0000000000000598 T _init
w _ITM_deregisterTMCloneTable
w _ITM_registerTMCloneTable
w _Jv_RegisterClasses
U printf
C库中可以找到foo函数符号和exam函数符号,再看看C++动态库libcppapi.so 的符号表
# nm -D libcppapi.so 0000000000202088 B __bss_start
U __cxa_atexit
w __cxa_finalize
0000000000202088 D _edata
0000000000202090 B _end
0000000000000dc8 T _fini
w __gmon_start__
U __gxx_personality_v0
0000000000000a58 T _init
w _ITM_deregisterTMCloneTable
w _ITM_registerTMCloneTable
w _Jv_RegisterClasses
U __stack_chk_fail
U _Unwind_Resume
0000000000000c50 T _Z3fooSs
0000000000000d17 T _Z4examPc
U _ZNSaIcEC1Ev
U _ZNSaIcED1Ev
U _ZNSolsEPFRSoS_E
U _ZNSsC1EPKcRKSaIcE
U _ZNSt8ios_base4InitC1Ev
U _ZNSt8ios_base4InitD1Ev
U _ZSt4cout
U _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_
U _ZStlsIcSt11char_traitsIcESaIcEERSt13basic_ostreamIT_T0_ES7_RKSbIS4_S5_T1_E
U _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
找到foo和exam函数的符号表变成了_Z3fooSs和_Z4examPc,因此使用C++写的库函数在对外提供Python调用的接口是需要转换成C接口,需要对源代码做适当的处理.
//cpp2capi.cpp
#include <iostream>
//Macro definition EXPORT_C_API is true export c api, otherwise cpp api
#define EXPORT_C_API true
//notify EXPORT_C_API when compiled
#if EXPORT_C_API
#warning("libcpp2capi export c api")
#else
#warning("libcpp2capi export cpp api")
#endif
#if EXPORT_C_API
namespace cppapi{
#endif
//cpp api follow
//----------------------------------------------------
std::string foo(std::string in)
{
std::cout << "foo function input: " << in << std::endl;
return "OK";
}
char* exam(char *in)
{
std::cout << "exam function input: " << in << std::endl;
return (char*)"OK";
}
//--------------------------------------------------
//cpp api above
#if EXPORT_C_API
}
extern "C" {
#include <string.h>
//convert string to char*
char* convert(std::string str)
{
std::cout << "convert " << str << "..." << std::endl;
int length = str.length();
char* p_char = new char[length+1];
memcpy(p_char, str.c_str(), length);
strcat(p_char, "\0");
return p_char;
}
char* foo(char* in)
{
std::cout << "foo(" << in << ")" << std::endl;
std::string ret = cppapi::foo(in);
return convert(ret);
}
char* exam(char *in)
{
return cppapi::exam(in);
}
}
#endif
然后编译cpp2capi.cpp:
# g++ -o libcpp2capi.so -shared -fPIC cpp2capi.cpp
cpp2capi.cpp:9:2: warning: #warning ("libcpp2capi export c api") [-Wcpp]
#warning("libcpp2capi export c api")
^
# ls
cpp2capi.cpp libcpp2capi.so pycall.py
# python pycall.py
foo(good)
foo function input: good
convert OK...
exam function input: good
success!
调用成功,查看libcpp2capi.so动态库中的符号表
# nm -D libcpp2capi.so
00000000002020d0 B __bss_start
0000000000001089 T convert
U __cxa_atexit
w __cxa_finalize
00000000002020d0 D _edata
00000000002020d8 B _end
00000000000012ae T exam
0000000000001328 T _fini
0000000000001137 T foo
w __gmon_start__
U __gxx_personality_v0
0000000000000cf0 T _init
w _ITM_deregisterTMCloneTable
w _ITM_registerTMCloneTable
w _Jv_RegisterClasses
U memcpy
w __pthread_key_create
U __stack_chk_fail
U _Unwind_Resume
0000000000000f70 T _ZN6cppapi3fooESs
0000000000001037 T _ZN6cppapi4examEPc
U _Znam
U _ZNKSs5c_strEv
U _ZNKSs6lengthEv
U _ZNSaIcEC1Ev
U _ZNSaIcED1Ev
U _ZNSolsEPFRSoS_E
U _ZNSsC1EPKcRKSaIcE
U _ZNSsC1ERKSs
U _ZNSsD1Ev
U _ZNSt8ios_base4InitC1Ev
U _ZNSt8ios_base4InitD1Ev
U _ZSt4cout
U _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_
U _ZStlsIcSt11char_traitsIcESaIcEERSt13basic_ostreamIT_T0_ES7_RKSbIS4_S5_T1_E
U _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
符号表中存在foo和exam函数符号.
当然也可以使用:
# objdump -T libcpp2capi.so
libcpp2capi.so: file format elf64-x86-64
DYNAMIC SYMBOL TABLE:
0000000000000dd0 l d .init 0000000000000000 .init
0000000000000000 w D *UND* 0000000000000000 __gmon_start__
0000000000000000 w D *UND* 0000000000000000 _Jv_RegisterClasses
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4 _Znam
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4.21 _ZNKSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE6lengthEv
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4 _ZNSt8ios_base4InitC1Ev
0000000000000000 DF *UND* 0000000000000000 GLIBC_2.2.5 __cxa_atexit
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4 _ZNSt8ios_base4InitD1Ev
0000000000000000 w D *UND* 0000000000000000 _ITM_deregisterTMCloneTable
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4 _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
0000000000000000 w D *UND* 0000000000000000 _ITM_registerTMCloneTable
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4.21 _ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEED1Ev
0000000000000000 w DF *UND* 0000000000000000 GLIBC_2.2.5 __cxa_finalize
0000000000000000 DO *UND* 0000000000000000 GLIBCXX_3.4 _ZSt4cout
0000000000000000 DF *UND* 0000000000000000 GLIBC_2.4 __stack_chk_fail
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4 _ZNSaIcED1Ev
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4 _ZNSolsEPFRSoS_E
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4.21 _ZNKSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE5c_strEv
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4 _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4.21 _ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEC1ERKS4_
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4.21 _ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEC1EPKcRKS3_
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4 _ZNSaIcEC1Ev
0000000000000000 DF *UND* 0000000000000000 CXXABI_1.3 __gxx_personality_v0
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4.21 _ZStlsIcSt11char_traitsIcESaIcEERSt13basic_ostreamIT_T0_ES7_RKNSt7__cxx1112basic_stringIS4_S5_T1_EE
0000000000000000 DF *UND* 0000000000000000 GCC_3.0 _Unwind_Resume
0000000000000000 DF *UND* 0000000000000000 GLIBC_2.14 memcpy
0000000000001207 g DF .text 0000000000000177 Base foo
000000000000137e g DF .text 000000000000001a Base exam
00000000002020c8 g D .bss 0000000000000000 Base _end
00000000002020c0 g D .data 0000000000000000 Base _edata
0000000000001159 g DF .text 00000000000000ae Base convert
00000000002020c0 g D .bss 0000000000000000 Base __bss_start
0000000000000dd0 g DF .init 0000000000000000 Base _init
00000000000013f8 g DF .fini 0000000000000000 Base _fini
0000000000001040 g DF .text 00000000000000c7 Base _ZN6cppapi3fooENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE
0000000000001107 g DF .text 0000000000000052 Base _ZN6cppapi4examEPc