std::string::assign() in C++
Last Updated :
28 Oct, 2020
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
#include <iostream>
#include <string>
using namespace std;
void assignDemo(string str1, string str2)
{
str1.assign(str2);
cout << "After assign() : ";
cout << str1;
}
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
#include <iostream>
#include <string>
using namespace std;
void assignDemo(string str1, string str2)
{
str1.assign(str2, 5, 8);
cout << "After assign() : ";
cout << str1;
}
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
#include <iostream>
#include <string>
using namespace std;
void assignDemo(string str)
{
str.assign("GeeksforGeeks");
cout << "After assign() : ";
cout << str;
}
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
#include <iostream>
#include <string>
using namespace std;
void assignDemo(string str)
{
str.assign("GeeksforGeeks", 5);
cout << "After assign() : ";
cout << str;
}
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
#include <iostream>
#include <string>
using namespace std;
void assignDemo(string str)
{
str.assign(10, 'x');
cout << "After assign() : ";
cout << str;
}
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
#include <iostream>
#include <string>
using namespace std;
void assignDemo(string str)
{
string str1;
str1.assign(str.begin()+6, str.end()-0);
cout << "After assign() : ";
cout << str1;
}
int main()
{
string str("Hello World!");
cout << "Original String : " << str << endl;
assignDemo(str);
return 0;
}
|
Output:
Original String : Hello World!
After assign() : World!
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