不知道很多关于ctypes的，最近刚开始使用它。
我在类C的dll一个简单的函数返回一个指向动态生成的字符串。
它工作正常，但是，因为我手动分配内存的字符串，我应该在使用后释放它。
我有这样的事情：
extern "C" char* DLL_EXPORT func(const char* str1, const char* str2)
{
return getSomeString(str1, str2);
}
// Goal is to call this function correctly from Python.
extern "C" void DLL_EXPORT freeMem(void *mem)
{
if(mem!=NULL)
delete mem;
}
但我没有任何想法，我怎么可以通过在Python收到指针回来进行删除吗？
你在正确的轨道上。
// TestDLL.cpp
#include <string.h> // strcpy
extern "C" __declspec(dllexport) char* stringdup(const char* str) {
char* p = new char[strlen(str)+1];
strcpy(p,str);
return p;
}
// if you have no good reason to use void*, use the type
// you've allocated. while it usually works for built-in
// types, it wouldn't work for classes (it wouldn't call
// the destructor)
extern "C" __declspec(dllexport) void stringfree(char* ptr) {
// you don't need to check for 0 before you delete it,
// but if you allocate with new[], free with delete[] !
delete [] ptr;
}
而在蟒蛇：
# Test.py
import ctypes
lib = ctypes.cdll.TestDLL
# this creates a c-style char pointer, initialized with a string whose
# memory is managed by PYTHON! do not attempt to free it through the DLL!
cstr = ctypes.c_char_p("hello ctypes")
# call the dll function that returns a char pointer
# whose memory is managed by the DLL.
p = lib.stringdup(cstr)
# p is just an integer containing the memory address of the
# char array. therefore, this just prints the address:
print p
# this prints the actual string
print ctypes.c_char_p(p).value
# free the memory through the DLL
lib.stringfree(p)
通常，每次在使用功能ctypes应该有它的参数和返回类型声明所以Python可以检查正确的参数数量和类型转换Python对象参数传递给正确的C数据对象。 不幸的是在这种情况下，正常的返回值func会c_char_p ，但ctypes尝试是有益的，一个转换c_char_p返回值到Python字符串，还能访问原始的C指针值。 相反，你可以声明返回类型c_void_p和使用cast检索字符串值，其离开返回值的c_char_p对象。
下面是一个示例（Python 3）：
import ctypes
func = ctypes.cdll.TestDLL.func
func.argtypes = [ctypes.c_char_p,ctypes.c_char_p]
func.restype = ctypes.c_void_p
freeMem = ctypes.cdll.TestDLL.freeMem
freeMem.argtypes = [ctypes.c_void_p]
freeMem.restype = None
s = func(b'abcdef',b'ghijkl')
s = ctypes.cast(s,ctypes.c_char_p)
print(s.value)
freeMem(s)
