std::basic_string<CharT,Traits,Allocator>::resize

 

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std::basic_string

Member functions basic_string::basic_string basic_string::~basic_string basic_string::operator= basic_string::assign basic_string::assign_range (C++23) basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (DR*) basic_string::back (DR*) basic_string::data basic_string::c_str basic_string::operator  basic_string_view (C++17) Iterators basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (DR*) Modifiers basic_string::clear basic_string::insert basic_string::insert_range (C++23) basic_string::erase basic_string::push_back basic_string::pop_back (DR*) basic_string::append basic_string::append_range (C++23) basic_string::operator+= basic_string::replace basic_string::replace_with_range (C++23) basic_string::copy basic_string::resize basic_string::resize_and_overwrite (C++23)   basic_string::swap

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	(1)
void resize( size_type count );			(until C++20)
constexpr void resize( size_type count );			(since C++20)
		(2)
void resize( size_type count, CharT ch );				(until C++20)
constexpr void resize( size_type count, CharT ch );				(since C++20)

Resizes the string to contain count characters.

If the current size is less than count, additional characters are appended:

1) Initializes appended characters to CharT().

2) Initializes appended characters to ch.

If the current size is greater than count, the string is reduced to its first count elements.

Parameters

count	-	new size of the string
ch	-	character to initialize the new characters with

Return value

(none)

Exceptions

std::length_error if count > max_size(). Any exceptions thrown by corresponding Allocator.

If an exception is thrown for any reason, this function has no effect (strong exception guarantee).(since C++11)

Example

Run this code

#include <iostream>
#include <iomanip>
#include <stdexcept>
 
int main()
{
    const unsigned  desired_length{ 8 };
    std::string     long_string( "Where is the end?" );
    std::string     short_string( "H" );
 
 
    std::cout << "Basic functionality:\n"
              << "Shorten:\n"
              << "1. Before: " << quoted( long_string ) << '\n';
    long_string.resize( desired_length );
    std::cout << "2. After:  " << quoted( long_string ) << '\n';
 
 
    std::cout << "Lengthen with a given value 'a':\n"
              << "3. Before: " << quoted( short_string ) << '\n';
    short_string.resize( desired_length, 'a' );
    std::cout << "4. After:  " << quoted( short_string ) << '\n';
 
 
    std::cout << "Lengthen with char() == " << static_cast<int>(char()) << '\n'
              << "5. Before: " << quoted( short_string ) << '\n';
    short_string.resize( desired_length + 3 );
    std::cout << "6. After:  \"";
    for (char c : short_string) {
        std::cout << (c == char() ? '@' : c);
    }
    std::cout << "\"\n\n";
 
 
    std::cout << "Errors:\n";
    {
        std::string s;
 
        try {
            // size is OK, no length_error
            // (may throw bad_alloc)
            s.resize(s.max_size() - 1, 'x');
        } catch (const std::bad_alloc& ex) {
            std::cout << "1. Exception: " << ex.what() << '\n';
        }
 
        try {
            // size is OK, no length_error
            // (may throw bad_alloc)
            s.resize(s.max_size(), 'x');
        } catch (const std::bad_alloc& ex) {
            std::cout << "2. Exception: " << ex.what() << '\n';
        }
 
        try {
            // size is BAD, throw length_error
            s.resize(s.max_size() + 1, 'x');
        } catch (const std::length_error& ex) {
            std::cout << "3. Length error: " << ex.what() << '\n';
        }
    }
}

Possible output:

Basic functionality:
Shorten:
1. Before: "Where is the end?"
2. After:  "Where is"
Lengthen with a given value 'a':
3. Before: "H"
4. After:  "Haaaaaaa"
Lengthen with char() == 0
5. Before: "Haaaaaaa"
6. After:  "Haaaaaaa@@@"
 
Errors:
1. Exception: std::bad_alloc
2. Exception: std::bad_alloc
3. Length error: basic_string::_M_replace_aux

See also

sizelength

returns the number of characters (public member function)