std::strstreambuf::overflow
< cpp | io | strstreambuf
protected: virtual int_type overflow (int_type c = EOF); |
||
后附字符 c
到缓冲的放置区,若可能则重分配。
1) 若
c==EOF
,则不做任何事2) 否则,若放置区拥有可用的写位置( pptr() < epptr() ),则如同用 *pptr()++ = c 存储该字符
3) 否则,若流缓冲模式非动态,或流当前为冻结,则函数失败并返回 EOF
4) 否则,函数重分配(或初始分配)足够大以保有当前动态数组(若存在)加至少一个额外写入位置的动态数组。若构造函数中使用了指向分配函数的指针
palloc
,则以 (*palloc)(n) 调用该函数,否则用 new char[n] ,其中 n
为要分配的字节数。若构造函数中使用了指向解分配函数的指针 pfree
,则以 (*pfree)(p) 调用该函数分配先前的数组,否则用 delete[] p ,若需要解分配。若分配失败,则函数失败并返回 EOF 。参数
c | - | 要存储于放置区的字符 |
返回值
若 c==EOF ,则返回异于 EOF 的某值。否则,成功时返回 (unsigned char)(c) ,失败时返回 EOF 。
示例
运行此代码
#include <strstream> #include <iostream> struct mybuf : std::strstreambuf { int_type overflow(int_type c) { std::cout << "Before overflow(): size of the put area is " << epptr()-pbase() << " with " << epptr()-pptr() << " write positions available\n"; int_type rc = std::strstreambuf::overflow(c); std::cout << "After overflow(): size of the put area is " << epptr()-pbase() << " with " << epptr()-pptr() << " write positions available\n"; return rc; } }; int main() { mybuf sbuf; // 读写动态 strstreambuf std::iostream stream(&sbuf); stream << "Sufficiently long string to overflow the initial allocation, at least " << " on some systems."; }
可能的输出:
Before overflow(): size of the put area is 16 with 0 write positions available After overflow(): size of the put area is 32 with 15 write positions available Before overflow(): size of the put area is 32 with 0 write positions available After overflow(): size of the put area is 64 with 31 write positions available Before overflow(): size of the put area is 64 with 0 write positions available After overflow(): size of the put area is 128 with 63 write positions available
参阅
[虚] |
从放置区写入字符到关联的输出序列 ( std::basic_streambuf<CharT,Traits> 的虚受保护成员函数) |
[虚] |
后附字符到输出序列 ( std::basic_stringbuf<CharT,Traits,Allocator> 的虚受保护成员函数) |
[虚] |
从放置区写字符到关联的文件 ( std::basic_filebuf<CharT,Traits> 的虚受保护成员函数) |
写一个字符到放置区域,并令 next 指针前进 ( std::basic_streambuf<CharT,Traits> 的公开成员函数) | |
插入字符 ( std::basic_ostream<CharT,Traits> 的公开成员函数) |