I have a C++ dll from other company. there is a method with a string& msg parameter, void methodA(string& msg);
What I have now is a char* with length which is big enough to take the msg from methodA. I want to call methodA to get message back from methodA.
Can I do it? how? thanks,
#include <algorithm>
void foo(char* buffer)
{
std::string str;
methodA(str);
std::copy(str.begin(), str.end(), buffer);
buffer[str.size()] = 0;
}
Sounds like you will need to use a pattern like this. It is unclear whether the paramter is an in/out or simply an out parameter. So you'll need one of these...
IN/OUT:
const char s[BIG_ENOUGH] = "whatever";
std::string str(s);
methodA(str);
// str should now have the response according to your API description
OUT:
std::string str;
methodA(str);
// str should now have the response according to your API description
// if you need to result in `s`...
strncpy(s, str.c_str(), BIG_ENOUGH);
s[BIG_ENOUGH - 1] = '\0'; // just to be safe
strncpy is possibly overly cautious.
Create a string out of your char* and pass it to methodA. That's how I'd do it.
Not sure what you're looking for here.
Note: Oh, I see it. Took me a moment.
std::string my_msg;
methodA(my_msg);
strcpy(my_char_star, my_msg.c_str());
I do have to say that this is basically exactly the opposite of the kind of code you should be writing. You should be using std::string or std::vector to provide char* buffer arguments, not char* to replace std::string.
char buffer was "big enough" so I figured it didn't need mentioning, but you are of course right.
Yes you can.
#include <string>
void yourfunc( char * mymsg, int len ) {
string msg;
methodA(msg);
if( msg.length() < len ) {
strncpy( mymsg, msg.c_str(), len );
} else { // FAIL }
}
