python和C++能进行有效的交互,c++调用Python的一些小用法
写了一个python脚本导入发生异常,可能是编码问题(如存在中文),
Python默认的是ASCII
可加上:
#!/usr/bin/python
# -*- coding: utf-8 -*-
参见:https://www.python.org/dev/peps/pep-0263/
定义类C数据结构:
class Point(Structure):
_pack_ = 1
_fields_ = [('x', c_uint8),
('y', c_uint8),
]
定义点数组初始化:
pointList = [Point(0,0),
Point(1,1),
]
访问:pointList[i].x, pointList[i].y
也可强制转换为指针访问
pPoint = cast(addressof(point),POINTER(Point))
指针有一个属性contents为实例对象
pPoint.contents.x, pPoint.contents.y
想要定义数组:
class Array(Structure):
_pack_ = 1
_fields_ = [('iArray', c_uint8 * 5),
('bArray', c_ubyte * 5),
]
定义缓冲区:
buf = c_buffer("Hello",520)
buf = create_string_buffer("Hello", 10)
第二个是新一点的,旧的也可以用
ctypes的数据类型:https://docs.python.org/2/library/ctypes.html#ctypes.c_ubyte
addressof(obj): 获取ctypes类型地址
byref(obj, offset):
返回ctypes类型轻量级指针
对应以下C代码:(((char *)&obj) + offset)
sizeof: 计算变量和类型的字节数
调用c库的一些函数:
libc = cdll.msvcrt
fopen = libc.fopen
fwrite = libc.fwrite
fclose = libc.fclose
fseek = libc.fseek
fread = libc.fread
ftell = libc.ftell
memset = libc.memset
memcpy = libc.memcpy
可获取函数地址,调用与C一样,注意这些函数操作需要地址
可以用addressof获取ctypes类型的地址
接收C++传来的参数:
如果传过来的是Unicode字符需要转换为python字符串,否则会出现意想不到的错误
虽然用打印和写入文件的方式写入param内容是正确的,但是实际调用libc库时仍会
找不到路径
str(unicode(param))
使用python时如果更加了解其内在机制,会对使用该语言更有帮助
下面上代码:
1 #!/usr/bin/python 2 # -*- coding: utf-8 -*- 3 import os, sys 4 from ctypes import * 5 6 class CPoint(Structure): 7 _pack_ = 1 8 _fields_ = [('x', c_uint8), 9 ('y', c_uint8), 10 ] 11 12 class CArray(Structure): 13 _pack_ = 1 14 _fields_ = [('iArray', c_uint8 * 5), 15 ('bArray', c_char * 5), 16 ] 17 18 def EditBuf(buf, len): 19 tmp = buf 20 i = 0 21 val = c_char('7') 22 while i < len: 23 memmove(addressof(tmp)+i,addressof(val),sizeof(val))#addressof(tmp)+i相当于指针移位 24 i += 1 25 26 libc = cdll.msvcrt 27 fopen = libc.fopen 28 fwrite = libc.fwrite 29 fclose = libc.fclose 30 fseek = libc.fseek 31 fread = libc.fread 32 ftell = libc.ftell 33 memset = libc.memset 34 memcpy = libc.memcpy 35 36 if __name__ == '__main__': 37 point = CPoint(5,6) 38 pPoint = cast(addressof(point),POINTER(CPoint)) 39 print "point.x = %d , point.y = %d" %(point.x, point.y) 40 print "pPoint.x = %d , pPoint.y = %d" %(pPoint.contents.x, pPoint.contents.y) 41 print point, pPoint.contents#这里两个地址值不一样说明系统为pPoint新申请了一个Point保存复制的值 42 43 pointList = [CPoint(0,1), 44 CPoint(2,3) 45 ] 46 print pointList[0].x, pointList[0].y#数组 47 48 iArr = (c_uint8 * 5)(5,6,7,8) 49 bArr = (c_char * 5)('a','b','c') 50 print bArr[:] 51 cArray = CArray(iArr, bArr[:])#c_uint8和c_char赋初始值的方式不同,具体还没研究 52 print cArray.iArray[:] 53 print cArray.bArray[:] 54 55 buf = c_buffer("12345",8)#类似c_char*8 56 print buf.value 57 EditBuf(buf,8)#修改buf值,对内存修改 58 print buf.value 59 memmove(addressof(buf),byref(c_char('a')),sizeof(c_char)) 60 print buf.value 61 62 #C库函数调用 63 fp =fopen("D:\pythonCallClib.txt","wb+") 64 fwrite(buf,1,sizeof(buf),fp)#77777777 65 fseek(fp,3,0) 66 fwrite(addressof(c_char('8')),1,1,fp) 67 fclose(fp) 68 69 #sizeof 70 print "c_uint8 = %d bytes, c_int = %d bytes, buf = %d bytes" %(sizeof(c_uint8), sizeof(c_int), sizeof(buf)) 71 72 #cast 可以将buf强制转换成我们自定义的类型 73 buf = create_string_buffer("abc",8) 74 p = cast(addressof(buf),POINTER(CPoint)) 75 print p.contents.x, p.contents.y 76