Error with initialization structure in C++

Question

I have this structure in my code. 'Compilable' part of code:

#define MONITOR_TOPKEY  HKEY_LOCAL_MACHINE
#define MONITOR_SUBKEY  TEXT("SOFTWARE\\WMyRegistry")
struct params {
    HKEY hMainKey;
    LPTSTR hSubKey;
    string path;
    bool* runflg;   
};
void _tmain(void) {
    bool work = true;
    string defaultPath = "HKEY_LOCAL_MACHINE";
    defaultPath += "\\";
    defaultPath += MONITOR_SUBKEY;
    params* defaultParams = (params*) malloc(sizeof (params));
    defaultParams->hMainKey = MONITOR_TOPKEY;
    defaultParams->hSubKey = MONITOR_SUBKEY;    
    defaultParams->path = defaultPath; // HERE THERE IS A PROBLEM
    defaultParams->runflg = &work;
}

When I set all parametrs (except "string") - all are good and working. But when I try to inizialize 'string' parametr (or another type instead of this, for ex myClass type or another else type variable) I have the error

"Unhandled exception at 0x0FDEEAD0 (msvcr110d.dll) in ConsoleApplication1.exe:
0xC0000005: Access violation when writing to the address 0xCDCDCDCD."

I don't understand, why doens't work " defaultParams->path = defaultPath". Can someone explain?

I bet some dollars that work is a (non-static) local variable... — user529758
– user529758, Commented Nov 20, 2013 at 18:53
Also, IDK how much of a problem that could be, but malloc() doesn't work well in C++, it doesn't call constructors. So a simple innocent-looking assignment may cause your program to try to deallocate garbage... — user529758
– user529758, Commented Nov 20, 2013 at 18:57
Also, show us some compilable code that actually fails. The question is too abstract as it is now. — Guilherme Bernal
– Guilherme Bernal, Commented Nov 20, 2013 at 19:11

MinandLucy · Accepted Answer · 2013-11-20 20:01:14Z

1

I think there may be something wrong with malloc. Because malloc just allocate some memory for the object. The string in your code may excess the boundary of the the memory you allocated. So there is access violation.

Try to use new instead of malloc.

answered Nov 20, 2013 at 20:01

MinandLucy

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1 Comment

alena_fox_spb Over a year ago

Thanks! Your advice were very usefull too

AndersK · Accepted Answer · 2013-11-20 20:07:04Z

0

You are using malloc on a struct with a C++ class std:string in it

malloc knows nothing about constructors so your string will not be initialized.

instead use new/delete and avoid using malloc/free in your C++ program

params* defaultParams = new params;

or preferably

std::unique_ptr<params> defaultParams(new params);

answered Nov 20, 2013 at 20:07

AndersK

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Preetam Singh · Accepted Answer · 2013-11-20 19:25:30Z

0

here you use a Registry class obj which initialize value second obj, you can't initialize obj without using assignment operator overload. first you should overload the assignment.

answered Nov 20, 2013 at 19:25

Preetam Singh

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