Concactinating Strings

This should be my last ExtDev question before an extension release.

I have tried numerous ways to concactinate two strings, but they all eventually fail. They either don't compile, crash the app, or return something strange.

In an expression, I need to retrieve a string parameter. I must concactinate a string to it then return it as the output of the expression.

Thanks again.

Are you able to return a string + using a string parameter at all? I had crashing issues with that before... I'm not really an advanced programmer so I don't think I can help you. I just know that ReturnString expects a const char*... but that shouldn't make it crash.

Two possible errors:
1. When returning a string, you must set the correct flags to make mmf understand it's a string.

2. If you create a std::string and return it (or actually the address to the string, c_str()), the object will be destroyed and mmf will try to access freed memory.

There is some function you can call to get MMF to allocate the memory for the string you are going to return, and MMF will free it once it's done with it. You should use that.

What function should I use?

if you use rSDK, ReturnStringSafe(str); should work...

My code:

Code:

---

EXPRESSION(
        /* ID */                        0,
        /* Name */                        "Name(",
        /* Flags */                        EXPFLAG_STRING,
        /* Params */                (1,EXPPARAM_STRING,"Parameter")
) {
        char * str1 = (char *)"1st String"
        char * str2 = (char *)ExParam(TYPE_STRING);
        const char * str3 = strcat(str1,str2);
        ReturnStringSafe(str3);
}

---

I test this by creating a String Object and, on startup, setting it to my object's expression using a random parameter. The application crashes at the start of the frame.

You can't do that. str1 is set to a constant, in write protected memory. It should crash on strcat.

You could use strdup("1st String").

Sorry, I don't understand what to do with the function you gave me. Where do I put it?

Quote:

---

Originally Posted by Jaffob

char * str1 = (char *)"1st String"

---

Missing a semi-colon :)
(Probably not the solution)

My code has a semicolon ;). When I copied it in I must have accidentially removed it.

If there was no semicolon, the code itself would not compile.

I know that, just pointing it out

Code:

---

EXPRESSION(
        /* ID */                        0,
        /* Name */                        "Name(",
        /* Flags */                        EXPFLAG_STRING,
        /* Params */                (1,EXPPARAM_STRING,"Parameter")
) {
        char * str1 = (char *)"1st String";
        char * str2 = (char *)ExParam(TYPE_STRING);
        char * str3 = rdPtr->rRd->GetStringSpace(strlen(str1) + strlen(str2) + 1);
        strcpy(str3, str1);
        strcat(str3, str2);
        ReturnString(str3);
}

---

Raw strings in C are a pain...
But you could also use C++ CStrings like this:

Code:

---

EXPRESSION(
        /* ID */                        0,
        /* Name */                        "Name(",
        /* Flags */                        EXPFLAG_STRING,
        /* Params */                (1,EXPPARAM_STRING,"Parameter")
) {
        CString str1 = "1st String";
        CString str2 = (char *)ExParam(TYPE_STRING);
        CString str3 = str1 + str2;
        ReturnStringSafe(str3.c_str());
}

---

With Dynasoft's code my extension does not compile. It seems like CString has not been included. How can I include it?

Can you tell I haven't used them for a while :P
I got CString (a microsoft specific thing) and string (the C++ standard one) confused. Replace all the CString in my code with string, and add:

Code:

---

#include <string>

---

EDIT: So this:
EDIT: No + operator, only += apparently, so change like this:
EDIT3: Scratch that last edit

Code:

---

#include <string>

EXPRESSION(
        /* ID */                        0,
        /* Name */                        "Name(",
        /* Flags */                        EXPFLAG_STRING,
        /* Params */                (1,EXPPARAM_STRING,"Parameter")
) {
        string str1 = "1st String";
        string str2 = (char *)ExParam(TYPE_STRING);
        string str3 = str1 + str2;
        ReturnStringSafe(str3.c_str());
}

---

There is a + operator for std::string.

It wasn't listed in the online c++ help I looked at.
EDIT: Changed my post back.

Thanks everyone (Especially Dynasoft for his code)! It works now.