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

 

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std::basic_string

成员函数 basic_string::basic_string basic_string::~basic_string basic_string::operator= basic_string::assign basic_string::assign_range (C++23)   basic_string::get_allocator 元素访问 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) 迭代器 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) 搜索 basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of

修改器 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 容量 basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (DR*) 操作 basic_string::compare basic_string::starts_with (C++20) basic_string::ends_with (C++20) basic_string::contains (C++23) basic_string::substr

常量 basic_string::npos 非成员函数 operator+ swap(std::basic_string) erase(std::basic_string)erase_if(std::basic_string) (C++20)(C++20) I/O operator<<operator>> getline 比较 operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) 数值转换 stoistolstoll (C++11)(C++11)(C++11) stoulstoull (C++11)(C++11)  stofstodstold (C++11)(C++11)(C++11) to_string (C++11) to_wstring (C++11) 字面量 operator""s (C++14) 辅助类 hash<std::basic_string> (C++11) Deduction guides (C++17)

 

	(1)
basic_string substr( size_type pos = 0, size_type count = npos ) const;			(until C++23) (constexpr since C++20)
constexpr basic_string     substr( size_type pos = 0, size_type count = npos ) const&;			(since C++23)
constexpr basic_string substr( size_type pos = 0, size_type count = npos ) &&;		(2)	(since C++23)

返回子字符串 [pos, pos + count)。如果请求的子字符串超出字符串的末尾，即 count 大于 size() - pos (例如，如果 count == npos)，则返回的子字符串为 [pos, size())。

1) 等效于 return basic_string(*this, pos, count);。

2) 等效于 return basic_string(std::move(*this), pos, count);。

参数

pos	-	要包含的第一个字符的位置
count	-	子字符串的长度

返回值

包含子字符串 [pos, pos + count) 或 [pos, size()) 的字符串。

异常

std::out_of_range 如果 pos > size()。

如果由于任何原因抛出异常，这些函数不起作用（强异常安全保证）。

复杂度

与 count 成线性关系。

注意

返回字符串的分配器是默认构造的：新的分配器可能不是 get_allocator() 的副本。

示例

运行此代码

#include <iostream>
#include <string>
 
int main()
{
    std::string a = "0123456789abcdefghij";
 
    // count is npos, returns [pos, size())
    std::string sub1 = a.substr(10);
    std::cout << sub1 << '\n';
 
    // both pos and pos + count are within bounds, returns [pos, pos + count)
    std::string sub2 = a.substr(5, 3);
    std::cout << sub2 << '\n';
 
    // pos is within bounds, pos + count is not, returns [pos, size())
    std::string sub4 = a.substr(a.size() - 3, 50);
    // this is effectively equivalent to
    // std::string sub4 = a.substr(17, 3);
    // since a.size() == 20, pos == a.size() - 3 == 17, and a.size() - pos == 3
 
    std::cout << sub4 << '\n';
 
    try
    {
        // pos is out of bounds, throws
        std::string sub5 = a.substr(a.size() + 3, 50);
        std::cout << sub5 << '\n';
    }
    catch (const std::out_of_range& ex)
    {
        std::cout << ex.what() << '\n';
    }
}

可能的输出

abcdefghij
567
hij
basic_string::substr: __pos (which is 23) > this->size() (which is 20)

缺陷报告

以下行为变更的缺陷报告被追溯应用于先前发布的 C++ 标准。

DR	应用于	已发布行为	正确行为
LWG 847	C++98	没有异常安全保证	添加了强异常安全保证

参见

copy	复制字符 (public member function)
sizelength	返回字符数 (public member function)
find	查找给定子字符串的首次出现 (public member function)
constexpr size_type npos [static]	特殊值 size_type(-1)，其确切含义取决于上下文
substr	返回子字符串 (public member function of std::basic_string_view<CharT,Traits>)