Question

如何用c++中的read函数读取文件中的数据？？？

Answer 1

Read函数定义
通过read函数将文件中的数据按照一定的长度读取出来并且存放在新的数组中。用于从文件中读取数据。
函数原型istream& read (char* s, streamsize n);
参数char* s取出数据的流向的char类型数组指针，streamsize n表示数组的长度

参看官方链接http://www.cplusplus.com/reference/istream/istream/read/?kw=read
Read函数使用例子
#include <iostream> // std::cout
#include <fstream> // std::ifstream

int main () {

std::ifstream is ("test.txt", std::ifstream::binary);
if (is) {
// get length of file:
is.seekg (0, is.end);
int length = is.tellg();
is.seekg (0, is.beg);

char * buffer = new char [length];

std::cout << "Reading " << length << " characters... ";
// read data as a block:
is.read (buffer,length);

if (is)
std::cout << "all characters read successfully.";
else
std::cout << "error: only " << is.gcount() << " could be read";
is.close();

// ...buffer contains the entire file...

delete[] buffer;
}
return 0;
}

Answer 2

先用int fd=open(“filepath”)打开文件；获得文件描述符
然后read（fd,buf,sizeof(buf)）;

Answer 3

#include <fstream>
istream& read( char* buffer, streamsize num );

ifstream fin( "/tmp/data.txt" );
ofstream fout( "/tmp/results.txt", ios::app );
while( fin >> temp )
fout << temp + 2 << endl;
fin.close();
fout.close();

楼上是Linux的