CODEWITHSUNDEEP
c++
Pepelee
Pepelee

Reputation: 453

Returning struct with const char* property

In this wrapper method, I return a DN_OPstruct, which has two const char* properties: TargetNode_Identifier and Name. For p/invoke, I have to stay with const char* - Type, std::string won't work:

DN_OPstruct getDnOperationIntern(const char* charGuid){
    DN_OPstruct op;
    UA_OPstruct _op;     
    _op = GetOPData(charGuid);
    op.direction = _op.direction;
    op.Name = _op.Name.toUtf8(); 
    op.TargetNode_Identifier = _op.TargetNode_Identifier.toUtf8();
    op.TargetNode_NamespaceIndex = _op.TargetNode_NamespaceIndex;
    op.Type_of_OP = _op.Type_of_OP;
    return op ;
}

As I read, you have to strcpy const char*s . Without such help, the pointers of the properties will lose thier reference and I get false properties. Example for strcpy:

strcpy(new char[output.size()], output.c_str());

How can implement this in my method?

Upvotes: 0

Views: 410

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726489

You shouldn't implement it in your method - instead, you should implement it in a separate function, and use it in all places where you need to make a copy of a string:

char *copyCString(const string& s) {
    char *res = new char[s.size()+1]; // Add 1 for null terminator
    strcpy(res, s.c_str());
    return res;
}

Now you can use this function to make copies as needed:

op.Name = copyCString(_op.Name); 
op.TargetNode_Identifier = copyCString(_op.TargetNode_Identifier);

You could start with const char*, too:

char *copyString(const char* s) {
    char *res = new char[strlen(s)+1]; // Add 1 for null terminator
    strcpy(res, s);
    return res;
}

Now you call it like this:

op.Name = copyString(_op.Name.toUtf8()); 
op.TargetNode_Identifier = copyString(_op.TargetNode_Identifier.toUtf8());

Of course you are responsible for deleting the copies when you are done:

delete[] op.Name;
delete[] op.TargetNode_Identifier;

It would be a good idea to define a function for this, too:

void freeCopiedString(char *s) {
    delete[] s;
}

Upvotes: 1

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