NAME

std::basic_string::resize - std::basic_string::resize

Synopsis

void resize( size_type count ); (until C++20)
constexpr void resize( size_type count ); (since C++20)
void resize( size_type count, CharT ch ); (1) (until C++20)
constexpr void resize( size_type count, CharT ch (2) (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() ('\0' if CharT is char).
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