memcpy problem

[amalshah71]

Hello,
The structure of my classes is :

String.h

class String
{
   public:
          String(char*);
          ~String();
   private:
           char* data;
}

String.cpp

#include "String.h"

String::String(char* data)
{
	int datalength=sizeof(data); // shows 4 bytes
	int stringdatalength=sizeof(String::data); // shows 4 bytes
	int mul=STRLEN(data)*sizeof(char); // shows 8 bytes
	     String::data=(char*)MALLOC(sizeof(String::data)+STRLEN(data)*sizeof(char));
	int newstringdatalength=sizeof(String::data); // shows 4 bytes
	MEMCPY(String::data,data,sizeof(data));
}

Main.cpp

int main()
{
   String x("abcd"); // shows "abcd"
   String y("abcdefghijk"); // shows "abcd" instead of "abcdefghijk"
   return 0;
}

While creating y object , the data pointer in the String class shows "abcd" instead of "abcdefghijk".

Now, logically String::data and data in the String constructor both shows it's respective size as 4 bytes.

checked out the memcpy API...it says n number of bytes are copied from source to destination.

However, it does not seem to happen here...what am i missing?

help appreciated
amal

[Zaita]

Why are you writing your own string class?

C++ has a string class already.

[jsmith]

You are confusing sizeof with strlen.

Look up strdup(), which will do what you want in 1 line of code.

[anders43]

String::String(char* data)
{
	int datalength=sizeof(data); 
	int stringdatalength=sizeof(String::data); // ??
	int mul=STRLEN(data)*sizeof(char); // shows 8 bytes
	     String::data=(char*)MALLOC(sizeof(String::data)+STRLEN(data)*sizeof(char));
	int newstringdatalength=sizeof(String::data); // shows 4 bytes
	MEMCPY(String::data,data,sizeof(data));
}

Srtring::String() : data(NULL) 
{
  ;
}

String::String(char* argData) 
{
  // copy 'data'
  if ( argData != NULL )
 {
    data = new char [strlen(argData)+1];
    strcpy( data, argData );
  }
}

String::~String()
{
   delete data;
}

general: avoid using C stuff when working with classes, use C++ new/delete

You need also a default ctor and an assignment op since you need this to do a "deep" copy. Also error handling should be in the code, i've left that out as well.

hth
Anders