Standard C++ Classes

Standard C++ Classes

Software development today is increasingly component based. C++ supports various kinds of software building blocks. The simplest of these is the function that we investigated in. A more powerful technique uses built-in and user designed software objects.

C++ is a object oriented programming language. An OO programming language allows the programmer to define, create, and manipulate objects.

String Objects

A string is a sequence of characters, most often used to represent words and names. The C++ standard library provides the class string which specifies string objects.

#include <string>

You may assign a literal character sequence to a string object via the familiar string quotation syntax: 

string name = "joe";
std::cout << name << '\n';
name = "jane";
std::cout << name << '\n';
string name1 = "joe", name2;
name2 = name1;
std::cout << name1 << " " << name2 << '\n';
  • operator[]—provides access to the value stored at a given index within the string
  • operator+=—appends a string or single character to the end of a string object
  • at—provides bounds-checking access to the character stored at a given index
  • length—returns the number of characters that make up the string • size — returns the number of characters that make up the string (same as length)
  • find — locates the index of a sub string within a string object •
  • substr — returns a new string object made of a sub string of an existing string object
  • empty — returns true if the string contains no characters; returns false if the string contains one or more characters
  • clear—removes all the characters from a string 
string word = "computer";
std::cout << "\"" << word << "\" contains " << word.length()
<< " letters." << '\n';
"computer" contains 8 letters.

We see that operator[] works exactly like its namesake in the std::vector class

Extracting the new string od-by from the string Good-bye AndroWep-Tutorials
Extracting the new string od-by from the string Good-bye AndroWep-Tutorials
#include <iostream>

#include <string>

int main() {
        // Declare a string object and initialize it
        std::string word = "fred";
        // Prints 4, since word contains four characters
        std::cout << word.length() << '\n';
        // Prints "not empty", since word is not empty
        if (word.empty())
            std::cout << "empty\n";
        else
            std::cout << "not empty\n";
        // Makes word empty
        word.clear();
        // Prints "empty", since word now is empty
        if (word.empty())
            std::cout << "empty\n";
        else
            std::cout << "not empty\n";
        // Assign a string using operator= method
        word = "good";
        // Prints "good"
        std::cout << word << '\n';
        // Append another string using operator+= method
        word += "-bye";
        // Prints "good-bye"
        std::cout << word << '\n';
        // Print first character using operator[] method
        std::cout << word[0] << '\n';
        // Print last character
        std::cout << word[word.length() - 1] << '\n';
        // Prints "od-by", the substring starting at index 2 of length 5
        std::cout << word.substr(2, 5);
        std::string first = "ABC", last = "XYZ";
        // Splice two strings with + operator
        std::cout << first + last << '\n';
        std::cout << "Compare " << first << " and ABC: ";
        if (first == "ABC")
            std::cout << "equal\n";
        else
            std::cout << "not equal\n";
        std::cout << "Compare " << first << " and XYZ: ";
        if (first == "XYZ")
           std::cout << "equal\n";
         else
           std::cout << "not equal\n";
}

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