Open In App

std::string::assign() in C++

The member function assign() is used for the assignments, it assigns a new value to the string, replacing its current contents. 
Syntax 1: Assign the value of string str. 

string& string::assign (const string& str)

str :  is the string to be assigned.
Returns : *this




// CPP code for assign (const string& str)
#include <iostream>
#include <string>
using namespace std;
  
// Function to demonstrate assign
void assignDemo(string str1, string str2)
{
    // Assigns str2 to str1
    str1.assign(str2);
    cout << "After assign() : ";
    cout << str1;
 
}
         
// Driver code
int main()
{
    string str1("Hello World!");
    string str2("GeeksforGeeks");
 
    cout << "Original String : " << str1 << endl;
    assignDemo(str1, str2);
  
    return 0;
}

Output: 

Original String : Hello World!
After assign() : GeeksforGeeks

Syntax 2: Assigns at most str_num characters of str starting with index str_idx. It throws out_of _range if str_idx > str. size(). 

string& string::assign (const string& str, size_type str_idx, size_type str_num)

str : is the string to be assigned.
str_idx : is the index number in str.
str_num : is the number of characters picked 
from str_idx to assign
Return : *this




// CPP code to illustrate
// assign(const string& str, size_type
// str_idx, size_type str_num)
  
#include <iostream>
#include <string>
using namespace std;
  
// Function to demonstrate assign
void assignDemo(string str1, string str2)
{
    // Assigns 8 characters from
    // 5th index of str2 to str1
    str1.assign(str2, 5, 8);
    cout << "After assign() : ";
    cout << str1;
 
}
         
// Driver code
int main()
{
    string str1("Hello World!");
    string str2("GeeksforGeeks");
 
    cout << "Original String : " << str1 << endl;
    assignDemo(str1, str2);
  
    return 0;
}

Output: 

Original String : Hello World!
After assign() : forGeeks

Syntax 3: Assign the characters of the C-string cstr. It throws length_error if the resulting size exceeds the maximum number of characters. 

string & string::assign (const char* cstr)

Assigns all characters of cstr up to but not including '\0'.
Returns : *this.
Note : that cstr may not be a null pointer (NULL).




// CPP code for assign (const char* cstr)
  
#include <iostream>
#include <string>
using namespace std;
  
// Function to demonstrate assign
void assignDemo(string str)
{
    // Assigns GeeksforGeeks to str
    str.assign("GeeksforGeeks");
    cout << "After assign() : ";
    cout << str;
 
}
         
// Driver code
int main()
{
    string str("Hello World!");
 
    cout << "Original String : " << str << endl;
    assignDemo(str);
  
    return 0;
}

Output: 

Original String : Hello World!
After assign() : GeeksforGeeks

Syntax 4: Assigns chars_len characters of the character array chars. It throws length_error if the resulting size exceeds the maximum number of characters. 

string& string::assign (const char* chars, size_type chars_len)

*chars : is the pointer to the array to be assigned.
chars_len : is the number of characters to be assigned from 
character array.
Note : that chars must have at least chars_len characters.
Returns : *this.




// CPP code to illustrate
// string& string::assign
// (const char* chars, size_type chars_len)
  
#include <iostream>
#include <string>
using namespace std;
  
// Function to demonstrate assign
void assignDemo(string str)
{
    // Assigns first 5 characters of
    // GeeksforGeeks to str
    str.assign("GeeksforGeeks", 5);
    cout << "After assign() : ";
    cout << str;
 
}
         
// Driver code
int main()
{
    string str("Hello World!");
 
    cout << "Original String : " << str << endl;
    assignDemo(str);
  
    return 0;
}

Output: 

Original String : Hello World!
After assign() : Geeks

Syntax 5: Assigns num occurrences of character c. It throws length_error if num is equal to string::npos 

string & string::assign (size_type num, char c)

num :  is the number of occurrences to be assigned.
c :  is the character which is to be assigned repeatedly. 
Throws length_error if the resulting size exceeds the maximum number(max_size) of characters.
Returns : *this.




// CPP code for string&
// string::assign (size_type num, char c)
  
#include <iostream>
#include <string>
using namespace std;
  
// Function to demonstrate assign
void assignDemo(string str)
{
    // Assigns 10 occurrences of 'x'
    // to str
    str.assign(10, 'x');
    cout << "After assign() : ";
    cout << str;
 
}
         
// Driver code
int main()
{
    string str("#########");
 
    cout << "Original String : " << str << endl;
    assignDemo(str);
  
    return 0;
}

Output: 

Original String : #########
After assign() : xxxxxxxxxx

Syntax 6: Assigns all characters of the range [beg, end). It throws length_error if range outruns the actual content of string. 

template <class InputIterator>
   string& assign (InputIterator first, InputIterator last)
first, last : Input iterators to the initial and final positions 
in a sequence.

Returns : *this.




// CPP code for string&
// string::assign (size_type num, char c)
  
#include <iostream>
#include <string>
using namespace std;
  
// Function to demonstrate assign
void assignDemo(string str)
{
    string str1;
     
    // Assigns all characters between
    // str.begin()+6 and str.end()-0 to str1
    str1.assign(str.begin()+6, str.end()-0);
    cout << "After assign() : ";
    cout << str1;
 
}
         
// Driver code
int main()
{
    string str("Hello World!");
 
    cout << "Original String : " << str << endl;
    assignDemo(str);
  
    return 0;
}

Output: 

Original String : Hello World!
After assign() : World!

If you like GeeksforGeeks(We know you do!) and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org.


Article Tags :
C++