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void resize( size_type count); | (1) | (constexpr since C++20) |
void resize( size_type count, CharT ch); | (2) | (constexpr since C++20) |
Resizes the string to containcount characters.
If the current size is less thancount, additional characters are appended:
CharT ischar).If the current size is greater thancount, the string is reduced to its firstcount elements.
Contents |
| count | - | new size of the string |
| ch | - | character to initialize the new characters with |
std::length_error ifcount> max_size() istrue.Any exceptions thrown by correspondingAllocator.
If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).
#include <iomanip>#include <iostream>#include <stdexcept> int main(){constunsigned 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: "<<std::quoted(long_string)<<'\n'; long_string.resize(desired_length);std::cout<<"2. After: "<<std::quoted(long_string)<<'\n'; std::cout<<"Lengthen with a given value 'a':\n"<<"3. Before: "<<std::quoted(short_string)<<'\n'; short_string.resize(desired_length,'a');std::cout<<"4. After: "<<std::quoted(short_string)<<'\n'; std::cout<<"Lengthen with char() == "<<static_cast<int>(char())<<'\n'<<"5. Before: "<<std::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(conststd::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(conststd::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(conststd::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() == 05. Before: "Haaaaaaa"6. After: "Haaaaaaa@@@" Errors:1. Exception: std::bad_alloc2. Exception: std::bad_alloc3. Length error: basic_string::_M_replace_aux
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 847 | C++98 | there was no exception safety guarantee | added strong exception safety guarantee |
| LWG 2250 | C++98 | the behavior was undefined if count> max_size() istrue | always throws an exception in this case |
| 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] |
