DLL Function returning a string

[madhatt30]

Ok, I'm pretty new to the C++ area but not to programming. I program in various other languages and some of the basics are the same but a lot of it is not. for example in my world strings are variables that hold text and with C++ it appears strings are Objects pointing to a memory location that hold the text. what I need is to take a function that takes std::string and returns a char * for example.

char * myFunction(std::string INMSG)
{
// add text message "some text here" and join with INMSG
// and then return the combined text in char *
}

any help with this is appreciated
thanks

[ne555]

std::string are variables that hold text.
¿what do you want a char* for?

[madhatt30]

Well i've tried to return the std::string and it causes the external application to crash. i've tried returning char * and it didn't crash at all but I couldn't build the string in the function. i've been able to return an int and a double but not a string. Oh i'm loading the DLL with a program called MetaTrader 4. am I doing this the wrong way?

[Moschops]

When you return the char*, are you taking steps to ensure that the memory it points to is not being released for other use (i.e. written over by something else)?

[madhatt30]

here is what works for me and i'll show what doesn't work for me

	char* XPortMsg(char * inmsg)
	{ 
		char * retVal = "Something here: "; // Returns "Something here:" in MetaTrader 4
		//char * retVal = "Something here: " + inmsg; Throws error in MetaTrader 4
		
		return retVal;
		
	}

[madhatt30]

Ok so what I want is something pretty simple

function outline is like this

	char* XPortMsg(string inmsg)
	{ 
//		// take the string and perform operations
		// assemble a string for example
		char* retVal = "USER: ";
		// then I want to take the string and 
		// assemble it like
		char* retVal2 = retVal + inmsg.c_str();
		return retVal2;
	}

[madhatt30]

ok so i've made some progress on my issue and i'm able to pass a string but.

char* XPortMsg(string inmsg)
	{ 
		char* s = "DLL Received: ";
		string m = string(s);

		char* p = new char[inmsg.length()+1]; 
		memcpy(p, inmsg.c_str(), inmsg.length()+1);
		string sa = m + p;

		char* ret = new char[sa.length()+1];
		memcpy(ret, sa.c_str(), sa.length()+1);
		
		return ret;
	}

in my program MetaTrader 4 the return is not consistent. the returning value is always

"DLL Received: " with a trailing character like a or d or t for example
"DLL Received: d"

or it returns what is expected

"DLL Received: Calling DLL" which is correct.

anyone know why or how I can fix it

[madhatt30]

ok, so I got it working the following is the code in case anyone else is interested

char* XPortMsg(char* inmsg)
	{
		char* mHeader = "DLL Received ";
		// retrieve the string and assign to variable
		char* msgHeader = new char[strlen(inmsg)+1];
		memcpy(msgHeader,inmsg,strlen(inmsg)+1);
		// end retrieve

		return msgHeader;
	}