vb调用DLL时，有VB6.EXE (Cipher.dll) 处有未经处理的异常:读取位置 0x00000000 时发生访问冲突

[qq_41716731]

用cpp写的DLL，在cpp调用时没有问题，但是在vb中调用时报错：VB6.EXE 中的 0x66c36314 (Cipher.dll) 处有未经处理的异常: 0xC0000005: 读取位置 0x00000000 时发生访问冲突
小弟才疏学浅，实在搞不明白了，请大家帮忙看看，感激不尽

Cipher.cpp

#include "stdafx.h"
#include "Cipher.h"


BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
					 )
{
	switch (ul_reason_for_call)
	{
	case DLL_PROCESS_ATTACH:
	case DLL_THREAD_ATTACH:
	case DLL_THREAD_DETACH:
	case DLL_PROCESS_DETACH:
		break;
	}
	return TRUE;
}
__declspec(dllexport) string __stdcall compress_wireless(string str)
{   int j,k,g,resend_buf[MAX_PACK_SIZE],wireless_buf[MAX_PACK_SIZE];
	static string array[MAX_PACK_SIZE],compress_data1,compress_data2;
    unsigned int compress_data;
    	
	for(unsigned int i=0;i<=str.length();i+=3){
	g =i/3; 
	array[g]=str.substr(i,2);}
	for(int h=0;h<=14;h++){
		stringstream ss_1;
		ss_1<<hex<<array[h];
		ss_1>>wireless_buf[h];
		ss_1.str("");
	}
    for(j=0;j<15;j++)  
		resend_buf[1+j]=wireless_buf[j];	
	for(j=0;j<14;j++){
		compress_data=wireless_buf[j]*0x100+wireless_buf[j+1];		    
		if((compress_data&0x8000)!=0)
			compress_data=((compress_data/0x100)^0x89)*0x100+compress_data%0x100;
		for(k=0;k<8;k++){
			compress_data<<=1;
			if((compress_data&0x8000)!=0)
			compress_data=((compress_data/0x100)^0x89)*0x100+compress_data%0x100;
		}
		wireless_buf[j+1]=compress_data/0x100;
	}
	for(k=0;k<7;k++){
		compress_data<<=1;
		if((compress_data&0x8000)!=0)
			compress_data=((compress_data/0x100)^0x89)*0x100+compress_data%0x100;
	}
	compress_data<<=1;
	stringstream ss_2;
	ss_2<<hex<<compress_data;
	ss_2>>compress_data1;
	compress_data2 = compress_data1.substr(0,2);
	transform(compress_data2.begin(),compress_data2.end(),compress_data2.begin(),towupper);
	return compress_data2;
}

Cipher.h

#pragma once
#include "targetver.h"
#include "stdafx.h"          
#include <windows.h>
#include <iostream>
#include <sstream>
#include <stdlib.h>
#include <string>
#include<algorithm>
using namespace std;
#define WIN32_LEAN_AND_MEAN   
#define MAX_PACK_SIZE 20

#ifdef CIPHER_EXPORTS
#define CIPHER_API __declspec(dllexport)
#else
#define CIPHER_API __declspec(dllimport)
#endif

// 此类是从 Cipher.dll 导出的

__declspec(dllexport) string __stdcall compress_wireless(string str);

Cipher.def

 LIBRARY Cipher
  EXPORTS compress_wireless

VB调用过程

Option Explicit
Private Declare Function compress_wireless Lib "C:\Users\Administrator\Desktop\Cipher\Debug\Cipher.dll" (ByVal p As String) As String

Private Sub Command1_Click()
Dim str As String
str = compress_wireless("80 66 0A 99 0B 28 0A 0D 0D 0D 0D 0D 0D 0D 00 ")
Text1..Text = str
End Sub

Private Sub Text1_Change()

End Sub

[舉杯邀明月]

感觉你在 VB中的API函数类型声明不正确。　 从 Cipher.cpp 代码第22行来看，我觉得API返回的值是“字符串首址指针”， 　　那么VB6中应该把函数返回值声明为 Long 类型。 然后，直接按返回的指针值，直接Copy “MAX_PACK_SIZE”字节的数据到一个Byte数组中。

// 数据类型的定义：
static string array[MAX_PACK_SIZE],compress_data1,compress_data2;

// API的返回：
return compress_data2;

如果这“返回数据”都是有效的ASCII字符， 　　可以用Strconv( )函数把它从 Byte数组转换成字符串，再赋值给 TextBox控件。

[赵4老师]

崩溃的时候在弹出的对话框按相应按钮进入调试，按Alt+7键查看Call Stack即“调用堆栈”里面从上到下列出的对应从里层到外层的函数调用历史。双击某一行可将光标定位到此次调用的源代码或汇编指令处，看不懂时双击下一行，直到能看懂为止。

[sw519]

把vc的接口函数的所有string改成char*试试