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Difference between revisions of "cpp/string/basic string/resize"

From cppreference.com
< cpp‎ | string‎ | basic string
m (add shrink_to_fit() to see also section since it's related)
m ({{c}}, headers sorted, fmt)
Line 1: Line 1:
−
{{cpp/string/basic_string/title | resize}}
+
{{cpp/string/basic_string/title|resize}}
 
{{cpp/string/basic_string/navbar}}
 
{{cpp/string/basic_string/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
−
{{dcl rev multi | num=1
+
{{dcl rev multi|num=1
−
| until1=c++20 | dcl1=
+
|until1=c++20|dcl1=
 
void resize( size_type count );
 
void resize( size_type count );
−
| dcl2=
+
|dcl2=
 
constexpr void resize( size_type count );
 
constexpr void resize( size_type count );
 
}}
 
}}
−
{{dcl rev multi | num=2
+
{{dcl rev multi|num=2
−
| until1=c++20 | dcl1=
+
|until1=c++20|dcl1=
 
void resize( size_type count, CharT ch );
 
void resize( size_type count, CharT ch );
−
| dcl2=
+
|dcl2=
 
constexpr void resize( size_type count, CharT ch );
 
constexpr void resize( size_type count, CharT ch );
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
−
Resizes the string to contain {{tt|count}} characters.
+
Resizes the string to contain {{c|count}} characters.
  
−
If the current size is less than {{tt|count}}, additional characters are appended:
+
If the current size is less than {{c|count}}, additional characters are appended:
  
 
@1@ Initializes appended characters to {{c|CharT()}} ({{c|'\0'}} if {{tt|CharT}} is {{c|char}}).
 
@1@ Initializes appended characters to {{c|CharT()}} ({{c|'\0'}} if {{tt|CharT}} is {{c|char}}).
−
@2@ Initializes appended characters to {{tt|ch}}.
+
@2@ Initializes appended characters to {{c|ch}}.
  
−
If the current size is greater than {{tt|count}}, the string is reduced to its first {{tt|count}} elements.
+
If the current size is greater than {{c|count}}, the string is reduced to its first {{c|count}} elements.
  
 
===Parameters===
 
===Parameters===
−
 
 
{{par begin}}
 
{{par begin}}
−
{{par | count | new size of the string}}
+
{{par|count|new size of the string}}
−
{{par | ch | character to initialize the new characters with }}
+
{{par|ch|character to initialize the new characters with}}
 
{{par end}}
 
{{par end}}
  
Line 47: Line 46:
 
===Example===
 
===Example===
 
{{example
 
{{example
−
| code =
+
|code =
−
#include <iostream>
+
 
#include <iomanip>
 
#include <iomanip>
 +
#include <iostream>
 
#include <stdexcept>
 
#include <stdexcept>
  
 
int main()
 
int main()
 
{
 
{
−
     const unsigned desired_length{ 8 };
+
     const unsigned desired_length{8};
−
     std::string     long_string( "Where is the end?" );
+
     std::string long_string("Where is the end?");
−
     std::string     short_string( "H" );
+
     std::string short_string("H");
−
 
+
  
 
     std::cout << "Basic functionality:\n"
 
     std::cout << "Basic functionality:\n"
 
               << "Shorten:\n"
 
               << "Shorten:\n"
−
               << "1. Before: " << quoted( long_string ) << '\n';
+
               << "1. Before: " << quoted(long_string) << '\n';
−
     long_string.resize( desired_length );
+
     long_string.resize(desired_length);
−
     std::cout << "2. After:  " << quoted( long_string ) << '\n';
+
     std::cout << "2. After:  " << quoted(long_string) << '\n';
−
 
+
  
 
     std::cout << "Lengthen with a given value 'a':\n"
 
     std::cout << "Lengthen with a given value 'a':\n"
−
               << "3. Before: " << quoted( short_string ) << '\n';
+
               << "3. Before: " << quoted(short_string) << '\n';
−
     short_string.resize( desired_length, 'a' );
+
     short_string.resize(desired_length, 'a');
−
     std::cout << "4. After:  " << quoted( short_string ) << '\n';
+
     std::cout << "4. After:  " << quoted(short_string) << '\n';
−
 
+
  
 
     std::cout << "Lengthen with char() == " << static_cast<int>(char()) << '\n'
 
     std::cout << "Lengthen with char() == " << static_cast<int>(char()) << '\n'
−
               << "5. Before: " << quoted( short_string ) << '\n';
+
               << "5. Before: " << quoted(short_string) << '\n';
−
     short_string.resize( desired_length + 3 );
+
     short_string.resize(desired_length + 3);
 
     std::cout << "6. After:  \"";
 
     std::cout << "6. After:  \"";
−
     for (char c : short_string) {
+
     for (char c : short_string)
 
         std::cout << (c == char() ? '@' : c);
 
         std::cout << (c == char() ? '@' : c);
−
    }
 
 
     std::cout << "\"\n\n";
 
     std::cout << "\"\n\n";
−
 
  
 
     std::cout << "Errors:\n";
 
     std::cout << "Errors:\n";
 +
    std::string s;
 +
 +
    try
 
     {
 
     {
−
         std::string s;
+
         // 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 {
+
    try
−
            // size is OK, no length_error
+
    {
−
            // (may throw bad_alloc)
+
        // size is OK, no length_error
−
            s.resize(s.max_size() - 1, 'x');
+
        // (may throw bad_alloc)
−
        } catch (const std::bad_alloc& ex) {
+
        s.resize(s.max_size(), 'x');
−
            std::cout << "1. Exception: " << ex.what() << '\n';
+
    }
−
        }
+
    catch (const std::bad_alloc& ex)
 +
    {
 +
        std::cout << "2. Exception: " << ex.what() << '\n';
 +
    }
  
−
        try {
+
    try
−
            // size is OK, no length_error
+
    {
−
            // (may throw bad_alloc)
+
         // size is BAD, throw length_error
−
            s.resize(s.max_size(), 'x');
+
        s.resize(s.max_size() + 1, 'x');
−
        } catch (const std::bad_alloc& ex) {
+
    }
−
            std::cout << "2. Exception: " << ex.what() << '\n';
+
    catch (const std::length_error& ex)
−
         }
+
    {
−
 
+
        std::cout << "3. Length error: " << 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';
+
−
        }
+
 
     }
 
     }
 
}
 
}
−
| p=true
+
|p=true
−
| output=
+
|output=
 
Basic functionality:
 
Basic functionality:
 
Shorten:
 
Shorten:
Line 131: Line 132:
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/string/basic_string/dsc size}}
+
{{dsc inc|cpp/string/basic_string/dsc size}}
−
{{dsc inc | cpp/string/basic_string/dsc reserve}}
+
{{dsc inc|cpp/string/basic_string/dsc reserve}}
−
{{dsc inc | cpp/string/basic_string/dsc shrink_to_fit}}
+
{{dsc inc|cpp/string/basic_string/dsc shrink_to_fit}}
 
{{dsc end}}
 
{{dsc end}}
  
 
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
 
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Revision as of 10:26, 2 June 2023

 
C++
 
Strings library
 
std::basic_string
Member functions
(C++23)
Element access
(DR*)
(DR*)
(C++17)
Iterators
(C++11)
(C++11)
(C++11)
(C++11)
Capacity
(DR*)
Modifiers
(C++23)
(DR*)
(C++23)
(C++23)
basic_string::resize
(C++23)  
Search
Operations
(C++20)
(C++20)
(C++23)
Constants
Non-member functions
(C++20)(C++20)
I/O
Comparison
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Numeric conversions
(C++11)(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)(C++11)
(C++11)
(C++11)
Literals
(C++14)
Helper classes
(C++11)
Deduction guides (C++17)

 
(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() ('\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.

Contents

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 <iomanip>
#include <iostream>
#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

 returns the number of characters
(public member function) [edit]
reserves storage
(public member function) [edit]
(DR*)
 reduces memory usage by freeing unused memory
(public member function) [edit]
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