"Go" Python calls C function

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Python calls C function-fast class network
Http://www.cricode.com/359.html

Keyword: Python ctypes,python call Dll,python call C function
To save software development costs, software developers want to shorten the development time of the software, hoping to develop a stable product in a short period of time. Python is powerful, easy-to-use, and fast to develop application software. However, due to the limitations of Python's own execution speed, modules with higher performance requirements need to be developed using more efficient programming languages, such as C, where other modules of the system are developed quickly using Python, and the modules developed by the C language are integrated with those developed by Python. In this context, based on the Python language and C language of their respective characteristics, C language to expand the existing Python program, it seems very meaningful.
This article provides python to invoke an instance of the C function in the form of a link library. Mainly used in Python-provided ctypes implementations. Official Python tutorial Address: ctypes

Example one: Python calls C language so
The first step: Writing C functions, TESTLIB.C

#include <stdio.h>
void Myprint ()
{
printf ("Hello,www.cricode.com!n");
}
Step two: Compile the C function into a linked library

$ gcc-shared-wl,-soname,testlib-o Testlib.so-fpic TESTLIB.C
If you are in Mac OS X,
$ gcc-shared-wl,-install_name,testlib.so-o Testlib.so-fpic TESTLIB.C
Step three: Using C-link library functions in python, write Python code test.py as follows

Import cTYPES

Testlib = cTYPES. Cdll ('/path/to/testlib.so ')
Testlib.myprint ()

Fourth step: just run it

$ python test.py
hello,www.cricode.com!

Example two: The parameter type is a string (that is, the pointer is passed)
When the parameter type is a string in the C function, use the Create_string_buffer provided by cTYPES to create the buffer.

The first step: Writing the C function testlib1.c

#include <string.h>
int reverse (char* str)
{
int i,j,t;
for (I=0,j=strlen (str)-1;i<j;i++,j--) {
t = Str[i];
Str[i] = Str[j];
STR[J] = t;
}
return 0;
}
Step two: Compile the C function into a linked library

$ gcc-shared-wl,-soname,testlib1-o Testlib1.so-fpic testlib1.c

Step three: Using C-link library functions in python, write Python code test1.py as follows:

Import cTYPES

S0 = ' hello,www.cricode.com '
S1 = Ctypes.create_string_buffer (S0)
TESTLIB1 = cTYPES. Cdll ('./testlib1.so ')
Testlib1.reverse (S0)
print ' S0 is: ', S0
print ' S1 is: ', s1.value
Fourth step: just run it

$ python test1.py
S0 Is:moc.edocirc.www,olleh
S1 is:hello,www.cricode.com

Example three: parameters are pointers, arrays (pointers, arrays)
The first step: Writing the C function testlib2.c

void Arrayfunc (int *sum,int arr[4])
{
*sum = arr[0]+ arr[1]*2 + arr[2]*3 + arr[3]*4;
}
Step two: Compile the C function into a linked library

$ gcc-shared-wl,-soname,testlib2-o Testlib2.so-fpic testlib2.c

Step three: Use C-link library functions in Python,

Import cTYPES

result = Ctypes.c_int ()
Array = ctypes.c_int*4
Parray = Array (ctypes.c_int (1), Ctypes.c_int (2), Ctypes.c_int (3), Ctypes.c_int (4))

TESTLIB2 = cTYPES. Cdll ('./testlib2.so ')
#testlib2. Arrayfunc.argtypes=[ctypes.c_void_p,ctypes.c_int*4]
Testlib2.arrayfunc (Ctypes.pointer (Result), Parray)
Print ' result is: ', result.value
Fourth step: just run it

$ python test2.py
Result Is:17

The example four parameters are structural bodies
The first step: Writing the C function testlib3.c

Write the Python code test2.py as follows:

typedef struct{
int x;
int y;
}mystruct;
MyStruct Structfunc (mystruct a,mystruct B)
{
MyStruct s;
S.x = a.x + b.x;
S.y = A.y + b.y;
return s;
}

Step two: Compile the C function into a linked library

$ gcc-shared-wl,-soname,testlib3-o Testlib3.so-fpic testlib3.c

Step three: Using C-link library functions in python, write Python code test3.py as follows:

Import cTYPES

Class MyStruct (cTYPES. Structure):
_fields_ = [("X", Ctypes.c_int),
("Y", Ctypes.c_int)]

A = MyStruct (2,4)
b = MyStruct (4,6)
TESTLIB3 = cTYPES. Cdll ('./testlib3.so ')
#srestype Muste be setted to avoid segment fault
Testlib3.structFunc.restype = MyStruct
c = Testlib3.structfunc (A, B)
Print C.x,c.y
Fourth step: just run it

$ python test3.py
6 10
Example five use of the callback function
What is a callback function?

A callback function is defined by yourself, but you never call it a generic term for a class of functions.

"That is to say, you are a living Lei Feng, you are making a wedding dress for others"

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