問題描述

對ctypes了解不多，最近才開始接觸.

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

我在類 C 的 dll 中有一個簡單的函數(shù)，它返回指向動態(tài)生成的字符串的指針.
它工作正常，但是因為我為字符串手動分配了內存，所以我應該在使用后釋放它.

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.

我有這樣的事情:

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;
    }

但我不知道，如何將接收到的指針傳回以在 Python 中刪除?

But i don't have any idea, how can i pass received pointer back for deletion in Python?

推薦答案

你在正確的軌道上.

// 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; 
}

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)

這篇關于如何在ctypes中傳回指針?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！