Question

C++中getline()的作用什么，工作过程是怎样的？

C++中getline()的作用什么，工作过程是怎样的？
如下面程序：
#include<iostream>
#include<sstream>
#include<fstream>
using namespace std;
int main(){
ifstream in("aaa.txt");
for(string s; getline(in, s); ){
int a, sum=0;
for(istringstream sin(s); sin>>a; sum += a);
cout<<sum<<endl;
}
}

getline(in, s) 的作用是读一行数据吧？
这个函数是遇到回车就中止么？

Answer 1

从流in里面每次读取一行，遇到\n返回，string s里面不包含\n,也就是getline会把缓冲区里面的\n取出来，并且丢弃掉。

Answer 2

Extract strings from the input stream line-by-line.

template<class CharType, class Traits, class Allocator>
basic_istream<CharType, Traits>& getline(
basic_istream<CharType, Traits>& _Istr,
basic_string<CharType, Traits, Allocator>& _Str
);

template<class CharType, class Traits, class Allocator>
basic_istream<CharType, Traits>& getline(
basic_istream<CharType, Traits>& _Istr,
basic_string<CharType, Traits, Allocator>& _Str,
CharType _Delim
);

Parameters
_Istr
The input stream from which a string is to be extracted.

_Str
The string into which are read the characters from the input stream.

_Delim
The line delimiter.

Return Value
The first function returns getline( _Istr, _Str, _Istr.widen( '\n' ) ).

The second function replaces the sequence controlled by _Str with a sequence of elements extracted from the stream _Istr.

Remarks
In order of testing, extraction stops:

At end of file.

After the function extracts an element that compares equal to delim, in which case the element is neither put back nor appended to the controlled sequence.

After the function extracts str.max_size elements, in which case the function calls setstate(ios_base::failbit).

If the function extracts no elements, it calls setstate(failbit). In any case, it returns _Istr.

Requirements
Header: <string>

See Also
Reference
string::getline

Other Resources
<string> Members