std::strstreambuf::underflow
来自 cppreference.com
< cpp | io | strstreambuf
| protected: virtual int_type underflow(); |
(C++98 中已弃用) (C++26 中已移除) |
|
从缓冲区的获取区域读取下一个字符。
如果输入序列有可用的读取位置 (gptr() < egptr()，则返回 (unsigned char)(*gptr())。
否则，如果 pptr() 不为空并且 pptr() > egptr()（存在放置区域并且它位于获取区域之后），则通过将 egptr() 增加到 gptr() 和 pptr() 之间的某个值来扩展获取区域的末尾，以包含最近写入放置区域的字符，然后返回 (unsigned char)(*gptr())。
否则，返回 EOF 以指示失败。
内容 |
[编辑] 参数
(无)
[编辑] 返回值
获取区域中的下一个字符，在成功时为 (unsigned char)(*gptr())，在失败时为 EOF。
[编辑] 示例
运行此代码
#include <iostream> #include <strstream> struct mybuf : std::strstreambuf { int_type overflow(int_type c) { std::cout << "Before overflow(): size of the get area is " << egptr()-eback() << " size of the put area is " << epptr()-pbase() << '\n'; int_type rc = std::strstreambuf::overflow(c); std::cout << "After overflow(): size of the get area is " << egptr()-eback() << " size of the put area is " << epptr()-pbase() << '\n'; return rc; } int_type underflow() { std::cout << "Before underflow(): size of the get area is " << egptr()-eback() << " size of the put area is " << epptr()-pbase() << '\n'; int_type ch = std::strstreambuf::underflow(); std::cout << "After underflow(): size of the get area is " << egptr()-eback() << " size of the put area is " << epptr()-pbase() << '\n'; if (ch == EOF) std::cout << "underflow() returns EOF\n"; else std::cout << "underflow() returns '" << char(ch) << "'\n"; return ch; } }; int main() { mybuf sbuf; // read-write dynamic strstreambuf std::iostream stream(&sbuf); int n; stream >> n; stream.clear(); stream << "123"; stream >> n; std::cout << n << '\n'; }
可能的输出
Before underflow(): size of the get area is 0 size of the put area is 0 After underflow(): size of the get area is 0 size of the put area is 0 underflow() returns EOF Before overflow(): size of the get area is 0 size of the put area is 0 After overflow(): size of the get area is 0 size of the put area is 32 Before underflow(): size of the get area is 0 size of the put area is 32 After underflow(): size of the get area is 3 size of the put area is 32 underflow() returns '1' Before underflow(): size of the get area is 3 size of the put area is 32 After underflow(): size of the get area is 3 size of the put area is 32 underflow() returns EOF 123
[编辑] 另请参阅
| [virtual] |
从关联的输入序列读取字符到获取区域 ( std::basic_streambuf<CharT,Traits> 的虚拟受保护成员函数) |
| [virtual] |
返回输入序列中可用的下一个字符 ( std::basic_stringbuf<CharT,Traits,Allocator> 的虚拟受保护成员函数) |
| [virtual] |
从关联的文件读取 ( std::basic_filebuf<CharT,Traits> 的虚拟受保护成员函数) |
| 从输入序列读取一个字符，但不推进序列 ( std::basic_streambuf<CharT,Traits> 的公共成员函数) | |
| 提取字符 ( std::basic_istream<CharT,Traits> 的公共成员函数) |
