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 // 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 // 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 // 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 // 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 // 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 // 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!
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