std::string resize() 方法

自 C++20 起

// (1) Non const version only
constexpr void resize( size_type count );

// (2) Non const version only
constexpr void resize( size_type count, CharT ch );

直到 C++20

// (1) Non const version only
void resize( size_type count );

// (2) Non const version only
void resize( size_type count, CharT ch );

将字符串大小调整为包含 count 个字符。

如果当前大小小于 count，则会追加额外的字符

• (1) 将追加的字符初始化为 CharT() (如果 CharT 是 char 则为 '\0')。
• (2) 将追加的字符初始化为 ch。

重要

如果当前大小大于count，则字符串将被截断为前 count 个元素。

参数

• count - 字符串的新大小
• ch - 用于初始化新字符的字符

返回值

(无)

复杂度

重要

本节需要改进。您可以通过编辑此文档页面来帮助我们。

异常

如果 count > max_size()，则抛出std::length_error。任何由相应 Allocator 抛出的异常。

如果由于任何原因抛出异常，此函数无效（强异常保证）。 (自 C++11 起)

示例

Main.cpp

#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';
        }
    }
}

输出

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