C\C++语言24|综合理解类:字符串类的自定义

来看看C++的string类是如何实现的，里面涵盖了C++的诸多知识点。

1 头文件mystring.h

#ifndef MY_STRING_H_
#define MY_STRING_H_
#include <iostream.h>
/*
* The next line is used because Codewarrior has a conflict with
* the STL string. Make sure to put the #include of this file
* AFTER all the system includes.
*/
#define string String
class StringIndexOutOfBounds { };
class string
{
public:
	string( const char *cstring = "" ); // Constructor
	string( const string & str ); // Copy constructor
	~string( ) // Destructor
	{ delete [ ] buffer; }
	const string & operator= ( const string & rhs ); // Copy
	const string & operator+=( const string & rhs ); // Append
	const char *c_str( ) const // Return C-style string
	{ return buffer; }
	int length( ) const // Return string length
	{ return strLength; }
	char operator[]( int k ) const; // Accessor operator[]
	char & operator[]( int k ); // Mutator operator[]
	enum { MAX_LENGTH = 1024 }; // Maximum length for input string
private:
	char *buffer; // storage for characters
	int strLength; // length of string (# of characters)
	int bufferLength; // capacity of buffer
};
ostream & operator<<( ostream & out, const string & str ); // Output
istream & operator>>( istream & in, string & str ); // Input
istream & getline( istream & in, string & str ); // Read line
bool operator==( const string & lhs, const string & rhs ); // Compare ==
bool operator!=( const string & lhs, const string & rhs ); // Compare !=
bool operator< ( const string & lhs, const string & rhs ); // Compare <
bool operator<=( const string & lhs, const string & rhs ); // Compare <=
bool operator> ( const string & lhs, const string & rhs ); // Compare >
bool operator>=( const string & lhs, const string & rhs ); // Compare >=
#endif

2 实现文件mystring.cpp

#include <string.h>
#include "mystring.h"
string::string( const char * cstring )
{
	if( cstring == NULL )
		cstring = "";
	strLength = strlen( cstring );
	bufferLength = strLength + 1;
	buffer = new char[ bufferLength ];
	strcpy( buffer, cstring );
}
string::string( const string & str )
{
	strLength = str.length( );
	bufferLength = strLength + 1;
	buffer = new char[ bufferLength ];
	strcpy( buffer,str.buffer );
}
const string & string::operator=( const string & rhs )
{
	if( this != &rhs )
	{
		if( bufferLength < rhs.length( ) + 1 )
		{
			delete [ ] buffer;
			bufferLength = rhs.length( ) + 1;
			buffer = new char[ bufferLength ];
		}
		strLength = rhs.length( );
		strcpy( buffer, rhs.buffer );
	}
	return *this;
}
const string & string::operator+=( const string & rhs )
{
	if( this == &rhs )
	{
		string copy( rhs );
		return *this += copy;
	}
	int newLength = length( ) + rhs.length( );
	if( newLength >= bufferLength )
	{
		bufferLength = 2 * ( newLength + 1 );
		char *oldBuffer = buffer;
		buffer = new char[ bufferLength ];
		strcpy( buffer, oldBuffer );
		delete [ ] oldBuffer;
	}
	strcpy( buffer + length( ), rhs.buffer );
	strLength = newLength;
	return *this;
}
char & string::operator[ ]( int k )
{
	if( k < 0 || k >= strLength )
		throw StringIndexOutOfBounds( );
	return buffer[ k ];
}
char string::operator[ ]( int k ) const
{
	if( k < 0 || k >= strLength )
		throw StringIndexOutOfBounds( );
	return buffer[ k ];
}
ostream & operator<<( ostream & out, const string & str )
{
	return out << str.c_str();
}
istream & operator>>( istream & in, string & str )
{
	char buf[ string::MAX_LENGTH + 1 ];
	in >> buf;
	if( !in.fail( ) )
		str = buf;
	return in;
}
istream & getline( istream & in, string & str )
{
	char buf[ string::MAX_LENGTH + 1 ];
	in.getline( buf, string::MAX_LENGTH );
	if( !in.fail( ) )
		str = buf;
	return in;
}
bool operator==( const string & lhs, const string & rhs )
{
	return strcmp( lhs.c_str( ), rhs.c_str( ) ) == 0;
}
bool operator!=( const string & lhs, const string & rhs )
{
	return strcmp( lhs.c_str( ), rhs.c_str( ) ) != 0;
}
bool operator<( const string & lhs, const string & rhs )
{
	return strcmp( lhs.c_str( ), rhs.c_str( ) ) < 0;
}
bool operator<=( const string & lhs, const string & rhs )
{
	return strcmp( lhs.c_str( ), rhs.c_str( ) ) <= 0;
}
bool operator>( const string & lhs, const string & rhs )
{
	return strcmp( lhs.c_str( ), rhs.c_str( ) ) > 0;
}
bool operator>=( const string & lhs, const string & rhs )
{
	return strcmp( lhs.c_str( ), rhs.c_str( ) ) >= 0;
}

－End－