Ex4.3: Optional Substring

ex4.3/String.cc

@@ -1,6 +1,7 @@
 //String.cc
 #include "String.hh"
 
+#include <iostream>
 String operator+( const String& lhs, const String& rhs ) {
 	String result(lhs); // Copy lhs into res with constructor
 	result += rhs ; // Use operator+= function which is a member of the class
@@ -28,3 +29,65 @@ String& String::operator+=( const String& a ) {
 
 	  return *this ;
 }
+String& String::subString( int start, int stop ) {
+	/*
+	 * Return a substring
+	 *
+	 * if stop is negative, interpret as len - stop
+	 * if start is negative, set start = 0
+	 *
+	 * if start > stop, return reversed string
+	 */
+
+	bool reverse = 0;
+	int len = 0;
+	char * tmp;
+
+	// Higher than Range
+	if ( start > _len ) {
+	    start = _len ;
+	}
+
+	if ( stop > _len ) {
+	    stop = _len ;
+	}
+
+	// Lower than Range
+	if ( start < 0 ) {
+	    start = _len + start%_len ;
+	}
+	if ( stop < 0 ) {
+	    stop = _len + stop%_len ;
+	}
+
+	// Set length
+	len = stop - start;
+
+	if ( start > stop ) {
+	    // Make sure len is positive
+	    len = -1 * len ;
+	    reverse = 1;
+	}
+
+	// allocate
+	tmp = new char[ len - 1];
+	tmp[len] = '\0';
+
+	for ( int i = 0 ; i < len ; i++ )
+	{
+		if ( reverse )
+		{
+			tmp[i] = _s[ start - i ];
+		}
+		else
+		{
+			tmp[i] = _s[ start + i ];
+		}
+	}
+
+	// make it a String again
+	String * result = new String(tmp);
+	delete tmp;
+
+	return *result;
+}

ex4.3/String.hh

@@ -12,6 +12,8 @@ public:
   String& operator=( const String& a );
   String& operator+=( const String& a );
 
+  String& subString( int start, int stop );
+
   operator const char* const() { return data(); }
 
   int length() const { return _len ; }

ex4.3/main.cpp

@@ -1,6 +1,7 @@
+#include "String.hh"
+
 #include <iostream>
 #include <cstring>
-#include "String.hh"
 
 int main() {
 	String str("Blubaloo");
@@ -32,4 +33,10 @@ int main() {
 	String c("Almost Empty");
 
 	std::cout << "String '" << c.data() << "' is " << strlen(c) << " chars long." << std::endl;
+
+
+	// Substring
+	std::cout << "First five characters: " << c.subString(0, 5) << std::endl;
+	std::cout << "First five characters reversed: " << c.subString(5, 0) << std::endl;
+	std::cout << "Last five characters: " << c.subString(-5, -1) << std::endl;
 }