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String Class in C++

There is no native “string” data type in C++ but its <string> library class provides a string object that emulates a string data type. To make this available to a program, the library must be added with an #include <string> directive at the start of the program.

#include<string.h>using namespace std;
int main()
char str[50];
int len;
cout << "Enter an array or string : ":
len = strlen(str);
cout << "Length of the string is : " << len;
return 0;

Like the <iostream> class library, the <string> library is part of the std namespace that is used by the C++ standard library classes. That means that a string object can be referred to as std::string, or more simply as string when using namespace std; again the directive must be at the start of the program.

Initializing Strings

A string “variable” can be declared in the same way as other variables. The declaration may optionally initialized the variable using the = assignment operator, or it may be initialized later in the programAdditionally a string variable may be initialized by including a text string between parentheses after the variable name.

Text strings in C++ must always be enclosed with double quotes(“”).
Single quotes (‘’) are only used for character values of the char data type.

Any numeric values that are assigned to a string variable, are no longer a numeric data type, so attempting to add string values of “4” and “5” with the addition operator(+) would add up to “45” instead of 9.

Converting Strings to other Data Types

Arithmetic cannot be performed on numeric values assigned to string variables until they are converted to a numeric data type. Luckily, there is a C++ <sstream> library provides a “stringstream” object that acts as an intermediary to convert strings to other data types.

Other features of a string variable can be revealed by calling its size()capacity(), and empty() functions. Written below is short summary of other features.

  • string variable can be emptied by assigning it an empty string (=“”) or by calling its clear() function.
  • Multiple string values can be concatenated by the + operator
  • string can be can be appended to another string by the += operator or by calling its append() function.
  • string can be compared to another string by the == operator or by calling its append() function.
  • string can be assigned to a string variable using the = operator or by calling its assign() function.
  • The swap() function swaps the values of two string variables.
  • Substrings of a string can be sought with the find() function, or specialized functions such as find_first_of(), and a character retrieved from a specified index position by the at() function.

Next we will be focusing more on control structure of the flow such as while loops, do-while loops, and for loops in addition to using the switch case for complex conditional tests.



My name is Truong Thanh, graduated Master of Information Technology and Artificial Intelligent in Frankfurt University,Germany. I create this Blog to share my experience about life, study, travel...with friend who have the same hobbies.

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