SDK Question Access violation, oapiWriteScenario

[Bj]

Here is the problem;

Access violation reading location

This is it (shortened)

    string name = "hi";
        char * buff;
        name.push_back(NULL); //append 0 to string so string is 0 terminiated
        //name now == 'hi[null]'  //just to be sure- 
        strcpy(buff,name.c_str());
        oapiWriteScenario_string(scn,"NAMED",buff);

Before anyone asks, it still doesn't work when you remove the push_back.

Something like this works;

oapiWriteScenario_string(scn,"NAMED","babalu");

No other errors, any ideas?

 

[martins]

You never allocate space for buff.
Why do you want to copy the string in the first place, instead of using name.c_str() directly as the 3rd argument in oapiWriteScenario_string?

 

[Bj]

You never allocate space for buff.
Why do you want to copy the string in the first place, instead of using name.c_str() directly as the 3rd argument in oapiWriteScenario_string?

oop

The more obvious they are...

anyway, its because of compiler error;

'oapiWriteScenario_string' : cannot convert parameter 3 from 'const char *' to 'char *'


This works, Thanks :tiphat:

string name = "hi";
char * buff = new char[50];
strcpy(buff,name.c_str());

FILEHANDLE scn = oapiOpenFile ("TEST",FILE_APP,ROOT);

//oapiWriteScenario_string(scn,"NAMED",buff);
oapiWriteScenario_string(scn,"NAMED",name.c_str());

 

[dbeachy1]

You could also just do this:

string name = "hi";
oapiWriteScenario_string(scn,"NAMED", (char *)name.c_str());

...to cast away the constness there. In this case it is safe to do because oapiWriteScenario_string does not modify the string passed in.

In any case, if you use the "new->copy->write" sequence anyway, don't forget to free up buff when you're done with it. But all that is a lot less elegant than just typecasting it IMO.

 

[Hielor]

You could also just do this:

string name = "hi";
oapiWriteScenario_string(scn,"NAMED", (char *)name.c_str());

...to cast away the constness there. In this case it is safe to do because oapiWriteScenario_string does not modify the string passed in.

In any case, if you use the "new->copy->write" sequence anyway, don't forget to free up buff when you're done with it. But all that is a lot less elegant than just typecasting it IMO.

I'd recommend using const_cast so it's explicitly obvious what you're doing:

string name = "hi";
oapiWriteScenario_string(scn,"NAMED", const_cast<char *>(name.c_str()));

 

[Urwumpe]

Much better would be if Orbiters API would use correct "const" attributes for the call by reference parameters... but well, there are many good fixes for it. :lol:

 

[Enjo]

Yup, const correctness never hurts ...
I'd ask for this as a feature request.