如何将指针传回ctypes？ [英] How to pass pointer back in ctypes?

问题描述

不了解ctypes，只是最近开始使用它。

Don't know much about ctypes, just recently began working with it.

我有一个简单的函数在C-like dll，它返回一个指针动态生成的字符串。

它工作正常，但是，因为我手动分配内存的字符串，我应该释放它使用后。

I have a simple function in C-like dll which returns a pointer to the dynamically generated string.
It is working fine, but, because i manually allocated memory for the string, i should free it after use.

像这样：

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;
    }

但我不知道，

推荐答案

您在正确的轨道上。

// 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python中：

# 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)

这篇关于如何将指针传回ctypes？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！