Overloading custom string operator += in c++
I am working to recreate the various c++ types in order to better understand how they work. I am currently stuck on the += operator and can not find what the issue is with my declaration. Here is the code for my Class:
class String {
int size;
char * buffer;
public:
String();
String(const String &);
String(const char *);
int length(){return size;};
friend bool operator==(const String &, const String &);
friend bool operator<=(const String &, const String &);
friend bool operator<(const String &, const String &);
friend ostream & operator<<(ostream &, const String &);
char operator[](const int);
// friend String operator+=(const String &,const char * p);
friend String operator+=(const char * p);
};
I am getting these to work as planned with the exception of the += operator defined as:
String operator+=(const char * p){
int p_size = std::char_traits<char>::length(p);
int new_size = size+p_size;
char * temp_buffer;
temp_buffer = new char(new_size);
for(int i=0; i<size; i++){
temp_buffer[i] = buffer[i];
}
for(int i=size, j=0; j<p_size;i++,j++){
temp_buffer[i] = p[j];
}
delete buffer;
buffer = new char[new_size];
size = new_size;
for(int i=0; i<size; i++){
buffer[i] = temp_buffer[i];
}
return *this;
}
My errors are string.h:29: error: âString operator+=(const char*)â must have an argument of class or enumerated type string.cpp:28: error: âString operator+=(const char*)â must have an argument of class or enumerated type
Any info of what I am doing wrong during overloading is appreciated.
operator+= is a binary operator and thus requires two operands (eg myString += " str", , where myString and " str" are the operands).
However, you have an ill-formed operator+= , as it only accepts a single argument. Note that your operator+= is a stand-alone function (not a class method), with it returning a String and accepting a single const char* argument.
To solve your problem, make your operator+= a member function/method, because by then, you'll have an implicit this parameter, which will be used as the left hand side operand.
class String {
...
String& operator+=(const char * p);
};
and its definition
String& String::operator+=(const char * p) {
...
return *this;
}
Notice that you are now returning a reference to *this , and its return type changed to String& . These are in accordance to guidelines in Operator overloading .
CRITICAL UPDATE:
temp_buffer = new char(new_size);
Noooo! You are allocating a single char and initializing it to new_size , and that is not what you desire. Change it to brackets.
temp_buffer = new char[new_size];
Now, you are properly allocating an array of new_size number of char s. And please don't forget to delete[] all those you new[] .
The reason why the += operator works with c-strings is that std::string s have an implicit conversion constructor from c-strings.
Since you already have a conversion constructor, you should just make a += operator that takes a String .
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