c++函数式编程：统计文件字符串，文件流

头文件

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include <algorithm>
#include <vector>

统计方法

int count_lines(const std::string &filename)
{std::ifstream in{filename};return std::count(std::istreambuf_iterator<char>{in},std::istreambuf_iterator<char>{},'\n');
}

std::istreambuf_iterator

读取输入缓冲区，板参数只能是char和wchar_t类型，std::istreambuf_iterator{}即默认构造的为end，例子如下

读取字符串

void readString()
{std::istringstream ins{"abcd"};std::string str(std::istreambuf_iterator<char>{ins},std::istreambuf_iterator<char>{});std::cout<<str<<std::endl;
}

扩展：istringstream类用于执行C++风格的串流的输入操作

例子：分割被空格、制表符等符号分割的字符串，类型转换

    std::istringstream ins{"123 456 789"};int nTmp = 0;while(ins >> nTmp){std::cout<<nTmp<<std::endl;}

扩展：ostringstream 类用于执行C风格的串流的输出操作

void writeString()
{std::ostringstream os{"123 456",std::ios_base::ate};os << " 789";std::cout<<os.str()<<std::endl;
}

扩展： stringstream类同时可以支持C风格的串流的输入输出操作

void readwriteString()
{std::stringstream streeam;streeam << "123 ";streeam << "789";int nTmp = 0;while(streeam >> nTmp){std::cout<<nTmp<<std::endl;}std::cout<<streeam.str()<<std::endl;
}

读取所文件所有内容到字符串，包括\n等空白字符

void readAllText(const std::string &filename)
{std::ifstream in{filename};std::string str(std::istreambuf_iterator<char>{in},std::istreambuf_iterator<char>{});std::cout<<str<<std::endl;
}

读取所文件所有内容到容器，包括\n等空白字符

void readAllTextVec(const std::string &filename)
{std::ifstream in{filename};std::vector<char> vec{std::istreambuf_iterator<char>{in},std::istreambuf_iterator<char>{}};std::cout<<vec.size()<<std::endl;
}

有重载++、*

void readAllTextCount(const std::string &filename)
{unsigned int nCount = 0;std::ifstream in{filename};std::istreambuf_iterator<char>  it{in},end;for(;it != end;it++){if(*it == '\n'){nCount++;}}std::cout<<"nCount:"<<nCount<<std::endl;
}