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Stream operation

本文对stream的operation进行总结，其实这些operation所对应的就是stream的member function，stream包括:

stream class buffer area
input stream std::basic_istream get area
output stream std::basic_ostream put area

关于buffer area，参见./Buffe。

下面通过对它们的member function进行对比来进行学习。

Positioning operation

NOTE: member function的名称中的后缀对应的是buffer area。

set position indicator return position indicator buffer area
std::basic_istream seekg tellg get area
std::basic_ostream seekp tellp put area

需要重点学习的是 **set position indicator**类方法，

prototype
basic_ostream& seek*( pos_type pos ); sets the position indicator to absolute (relative to the beginning of the file) value pos
basic_ostream& seek*( off_type off, std::ios_base::seekdir dir ); sets the position indicator to offset off relative to dir

Example

来源: cppreference std::basic_ostream::seekp

#include <sstream>
#include <iostream>

int main()
{
    std::ostringstream os("hello, world");
    os.seekp(7);
    os << 'W';
    os.seekp(0, std::ios_base::end);
    os << '!';
    os.seekp(0);
    os << 'H';
    std::cout << os.str() << '\n';
}
// g++ test.cpp

输出:

Hello, World!

stackoverflow remove char from stringstream and append some data

NOTE: 这种需求是我们经常会碰到的

Example: 从std::stringstream中将最后一个元素剔除:

    static std::string Create(const char *TableName, const CStructRtti *StructRtti)
    {
        std::stringstream S;
        S << "CREATE TABLE IF NOT EXISTS " << TableName << " (";
        int FieldCount = StructRtti->GetFieldCount();
        for (const SFieldInfo &FieldInfo : StructRtti->GetFieldInfoList())
        {
            S << FieldInfo.m_sFieldName << " " << GetColunmType(FieldInfo.m_Type) << " ,";
        }
        S.seekp(-1, std::ios_base::end); // 剔除最后一个元素
        S << ")";
        return S.str();
    }