C++ Character Conversion Functions: char to int, char to string

This Tutorial Covers C++ Character Conversion Functions like Conversion of a Character to Integer or String & Character Array to String with Code Examples:

In C++, as we develop applications involving many types, it becomes necessary to convert from one type to another. We have already seen a few basic type conversions in our earlier tutorials.

We have also seen string conversions and conversion of numeric types to strings. Apart from the string conversion functions we have already seen, there are a few functions that are used to convert a character into other data types.

These are the functions that take a single character or a character array and then convert them to other data types.

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C++ Character conversion functions

C++ Character Conversion Functions

When it comes to single character conversion to integer or string and conversion of character array to string, the conversion functions slightly change from that of string conversion functions.

In this tutorial we will discuss the following conversions:

  • Conversion of Character to Integer (char to int C++)
  • Conversion of Character to String (char to string C++)
  • Conversion of Character Array to String

The first two conversions deal with a single character while the last conversion involves character array.

Convert Character To Integer – char to int

To convert a single character to an integer type we have two methods as stated below:

#1) By Casting

We can use casting operation to convert a single character to its integer equivalent. In this case, the ASCII equivalent of the character will be displayed.

Consider the following conversion,

char a = 'A';
 int num = (int) a;

In this case, ‘num’ will have the value 65 which is ASCII equivalent of character ‘A’.

Alternatively, we can use the following operation if we want to convert a number character to an integer value.

 char a = '2';
 int num = a-48;

Here, 48 is the ASCII value of 0. What is done here is the second line a-48 implicitly converts char a to its ASCII equivalent and then subtracts it from 48 (50-48) that results in integer value 2.

#2) Using stringstream

As already seen in the tutorial on string conversion functions, we can convert a single character represented as a stringstream object to an integer or any numeric value.

Given below is a code to demonstrate this.

#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main()
{
    stringstream str;
    
    str << "5"; int x; str >> x;
    cout<<"Converted value of character 5 :"<<x;
}

Output:

Converted value of character 5 :5

Convert Character To String – char to string 

There are various ways using which we can convert a single character to a string.

Let's discuss some of these methods.

#1) Using A Constructor Provided By String Class.

Function Prototype: string s(int n, char x);
Parameter(s):
n=> Size of the string to be generated.
x=> Character that is to be converted to a string.
Return Value: string obtained by conversion of character.
Description: The constructor of string class takes in the length of the string (n) and a single character as parameters and then converts the character to string.

Given below is a simple example to demonstrate the conversion of a single character to string.

#include<iostream>
#include <string>
using namespace std; 
  
int main() { 
  string str(1,'A');
  cout<<"The string obtained by converting single character : "<<str;
 
  return 0; 
}

Output:

The string obtained by converting single character: A

The above conversion is a simple one. We call the string constructor and specify the length of the string (first parameter) as 1 since we are converting a single character and the second parameter is the character to be converted to string (in this case ‘A’).

#2) Using std::string Operator = And +=

The std::string class operators, = and += are overloaded for characters. So we can use these operators to convert a single character to string.

This is demonstrated in the program shown below.

#include<iostream>
#include <string>
using namespace std; 
  
int main()
 { 
  string str;
  char c = 'B';
  str = 'C';
  str += c;
   
  cout<<"The string obtained by converting single character : "<<str;
 
  return 0; 
} 

Output:

The string obtained by converting single character : CB

In this program, we have used both the overloaded operators, =, and +=. We have declared a string object and then assigned a character to it using the = operator. Next we use += operator and assign another character to the string object.

We see that the second time the character actually gets concatenated to the already existing contents in the string object.

#3) Using Various Methods Of std:: string

std:: string class supports various overloaded methods using which we can pass a character to string that ultimately converts character to string.

Some of the methods of std:: string class is:

  • push_back

Function Prototype: void push_back (char c)
Parameter(s): c=> Character to be assigned to string
Return Value: returns void
Description: This function is overloaded for characters and it assigns a character to the end of the string.

  • append

Function Prototype: string& append (size_t n, char c)
Parameter(s):
n=> Number of times the character is to be appended.
c=> Character that is to be appended to the string.
Return Value: String obtained by conversion of character.
Description: Append function of std:: string takes two arguments. The first argument is the number of times the character is to be copied to the string. The second argument is the actual character to be copied. So the append function will assign those many copies of character to the string as specified in the first argument.

  • assign

Function Prototype: string& assign (size_t n, char c);
Parameter(s):
n=> Number of copies of the character.
c=> Character that is to be copied to string.
Return Value: String obtained by conversion of character.
Description: Assign function replaces the current string contents with n (first argument) copies of the character (second argument).

  • insert

Function Prototype: string& insert (size_t pos, size_t n, char c);
Parameter(s):
pos=> Position at the beginning of which characters are to be inserted.
n=> Number of copies of the character.
c=> Character that is to be inserted into the string.
Return Value: String obtained by conversion of character.
Description: This function inserts n(second argument) copies of character (third argument) at the beginning position of the string specified by pos(first argument).

Next, we will develop a program that demonstrates all the above functions of std::string class.

#include<iostream>
#include <string>
using namespace std; 
  
int main()
 { 
  string str;
  str.push_back('A');
  
  cout<<"push_back single character : "<<str<<endl;
  str="";
  str.append(1,'C');
 
  cout<<"append single character : "<<str<<endl;
  str="";
  str.assign(1,'D');
  cout<<"assign single character : "<<str<<endl;
  
  str.insert(0,1,'B');
  cout<<"insert single character : "<<str<<endl;
  return 0; 
}

Output:

push_back single character: A
append single character: C
assign single character : D
insert single character: BD

The above program demonstrates the push_back, append, assign and insert functions. The output shows the result or the string returned by each function.

#4) Using std::stringstream

We have already discussed the conversion of numerical types to a string using stringstream. The conversion of character to a string also follows the same principle when a stringstream class is used.

The given character is inserted into the stream and then the contents are written to the string.

Let's make this clear using a C++ program.

#include<iostream>
#include <string>
#include <sstream>
using namespace std; 
  
int main()
 { 
  string str;
  stringstream mystr;
 
  mystr<<'A'; mystr>>str;
  
  cout<<"The string obtained by converting single character : "<<str;
 
  return 0; 
}

Output:

The string obtained by converting a single character: A

We first insert the character into the stream object and then that buffer is written to the string object. Thus the output of the program shows the contents of the string object which is a single character.

Convert Character Array To String

The class std:: string has many methods that can come handy while dealing with character arrays. Hence it is advisable to convert character arrays to string objects and then use them so that we can write efficient programs.

There are two methods to convert the character array into a string as shown below.

#1) Using String Constructor

As already discussed for converting a single character into string, we can make use of string constructor to convert a character array to string.

Function prototype: string (const char* s);
Parameters: s=> null-terminated character array to be converted to string
Return Value: string=> converted string
Description: This overloaded constructor of std::string class takes the character array or C-string as an argument and returns the string.

The following program demonstrates this conversion.

#include <iostream>
#include <string>
using namespace std;
int main()
{    
    char myarray[] = {"Software Testing Help"};
    
    string mystr(myarray);
    
    cout<<"Converted string: "<<mystr;
}

Output:

Converted string: Software Testing Help

The above program is quite simple. All it takes is just one call to std:: string constructor to convert the given character array to string.

#2) Using = Overloaded Operator

Another approach to convert character array to string object is to use an overloaded operator =. In this we can directly assign the character array to string object using = operator and the contents will be passed to string.

The following example shows this.

#include <iostream>
#include <string>
using namespace std;
int main()
{
    
    char myarray[] = {"Software Testing Help"};
    
    string mystr;
    
    mystr = myarray;
    
    cout<<"Converted string: "<<mystr;
  
}

Output:

Converted string: Software Testing Help

The above program assigns the array directly to a string object using = operator that results in contents of character array being copied to string object.

Conclusion

We have seen various methods to convert a single character as well as character arrays to string objects. Since std:: string class has many functions that allow us to manipulate the strings efficiently, it is always helpful to work with character data by converting it first to strings.

We can also use stringstream class methods to convert character data into strings. In this, we first insert the data into the stream and then write this buffer to a string object.

In our subsequent tutorials, we will discuss a stringstream class and more library functions in C++ in detail.

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