Harvest Software - Programming - C/C++

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C++ String -

In C, strings are considered as array of character where in C++, strings are regarded as an object. With this new paradigm, strings in C++ can be very powerful since string object provides a set of useful function to modify the string easily.

Creating and Initializing C++ strings

It’s fairly easy to create strings in C++, below is the sample how to create and initialize strings. Don’t forget to put #include <string> header.

Source Code


#include < iostream >
#include < string >

using namespace std;

int main()
{
     string blank;
     string s1 = "First way";
     string s2("Second way");

     cout << blank << endl;
     cout << s1 << endl;
     cout << s2 << endl; 

     return 0;
}

Output


First way
Second way

Copying and Concatenating strings

With strings object it’s very easy to copy and concatenate strings. It’s also introduced how to use the string object’s substr() member function to create a substring. Below is the code sample.

Source Code


#include < iostream >
#include < string >

using namespace std;

int main()
{
     string blank;
     string s1 = "First way";
     string s2("Second way");

     cout << blank << endl;
     cout << s1 << endl;
     cout << s2 << endl; 

     return 0;
}

Output


C++ strings
C++ strings
C++
strings
I like C++
I like C++ strings

Note that substr() is overloaded.

substr(fromIndex, toIndex);
substr(fromIndex);

The first one gets the substring from index fromIndex to toIndex – 1. The second gets substring from fromIndex until the end of the string.

Filling strings with Characters

We can fill a string with n numbers of character. Below is the sample of filling string with character.

Source Code


#include <iostream>
#include <string>
using namespace std;

int main()
{
     string mask(5,'*');
     cout << mask << endl;
}

Output


*****

Additional note :
We can get the i-th position character of the string using index in brackets.

string s = “get character”;
s[0] would be ‘g’
s[4] would be ‘c’

More on string Operations

There are other string operations which are commonly used, such as append, insert, replace, etc. We will discuss them one by one. One of the C++ strings advantage is that the strings grow as they need. There are several functions to monitor and manage the strings’ size

size(); returns number of char stored
length(); identical to size();
capacity(); returns the size of current allocation
reserve(); specify certain amount for future usage
resize(); resize the strings’ size

Source code


#include <iostream>
#include <string>
using namespace std;

int main()
{
     string s = "C++ strings";

     cout << "Initial condition" << endl;
     cout << "Size : " << s.size() << endl;
     cout << "Capacity : " << s.capacity() << endl;

     s.reserve(100);

     cout << "After reserve" << endl;
     cout << "Size : " << s.size() << endl;
     cout << "Capacity : " << s.capacity() << endl;

     s.resize(20);

     cout << "After resize" << endl;
     cout << "Size : " << s.size() << endl;
     cout << "Capacity : " << s. capacity << endl;

     return 0;
}

Output


Initial Condition
Size : 11
Capacity : 31
After reserve
Size : 11
Capacity : 127
After resize
Size : 20
Capacity : 127

Append, Insert, Find and Replace

There are quite a number of overloaded versions of these operations. We will demonstrate the relatively more common one. The function find() will return string::npos if it doesn’t find the desired string.

Source Code


#include <iostream>
#include <string>
using namespace std;

int main()
{
     string s = "C++";
     string tag = "good";

     // append
     s.append(" is a good language");
     cout << s << endl;

     // insert
     s.insert(14,"programming");
     cout << s << endl;

     // find and replace
     int start = s.find(tag);
     s.replace(start,tag.size(),"powerful");
     cout << s << endl;

     return 0;
}

Output


C++ is a good language
C++ is a good programming language
C++ is a powerful programming language

Find and replace is a common operation that we usually use in text editing. Below we demonstrate how to replace all the occurrence of the word with a given word.

Source Code


#include <iostream>
#include <string>
using namespace std;

int main()
{
     string s = "All this will be replaced by this";
     string toFind = "this";
     string replaceWith = "that";

     // before find and replace
     cout << s << endl;

     // find and replace operation
     int pos;
     while ((pos = s.find(toFind)) != string::npos)
          s.replace(pos,toFind.size(),replaceWith);

     // after find and replace
     cout << s << endl;

     return 0;
}

Output


All this will be replaced by this
All that will be replaced by that