#include

#include

#include

read_file_by_line() {

infile.open("filepath");//方法1 open

//fstream infile2("filepath");//方法2 构造

//assert(infile.is_open());//判断文件是否打开

if (infile.is_open()==true)//file exist

{

while(!infile.eof())//未到句尾

{

string nline;

getline(infile,nline, '\n');//从文件中读一行给newline

//myfile.getline (buffer,80);

if(infile.fail()){//读取失败

break;

}

//nline存储等操作

}

} else{

//file not exist

}

infile.close();//关文件

infile.clear();//标志位清零

}

若是在没有成功打开文件后仍调用close(),会造成错误。

void clear (iostate state = goodbit);

Set error state flags

Sets a new value for the stream's internal error state flags.

(constructor) Construct object (public member function )

open Open file (public member function )

is_open Check if file is open (public member function )

close Close file (public member function )

member constant opening mode

app (append) Set the stream's position indicator to the end of the stream before each output operation.

ate (at end) Set the stream's position indicator to the end of the stream on opening.

binary (binary) Consider stream as binary rather than text.

in (input) Allow input operations on the stream.

out (output) Allow output operations on the stream.

trunc (truncate) Any current content is discarded, assuming a length of zero on opening.

bool fail() const;

Check whether failbit or badbit is set

Returns true if either (or both) the failbit or the badbit error state flags is set for the stream.

bool eof() const;

Check whether eofbit is set

Returns true if the eofbit error state flag is set for the stream.

basic_istream& getline (char_type* s, streamsize n );

basic_istream& getline (char_type* s, streamsize n, char_type delim);

Get line

Extracts characters from the stream as unformatted input and stores them into s as a c-string, 

until either the extracted character is the delimiting character, or n characters have been written to s (including the terminating null character).

The delimiting character is the newline character (widen('\n')) for the first form, and delim for the second: when found in the input sequence, 

it is extracted from the input sequence, but discarded and not written to s.

The function will also stop extracting characters if the end-of-file is reached. 

If this is reached prematurely (before either writing n characters or finding delim), the function sets the eofbit flag.

The failbit flag is set if the function extracts no characters, or if the delimiting character is not found once (n-1) characters have already been written to s. 

Note that if the character that follows those (n-1) characters in the input sequence is precisely the delimiting character, 

it is also extracted and the failbit flag is not set (the extracted sequence was exactly n characters long).

A null character (char_type()) is automatically appended to the written sequence if n is greater than zero, even if an empty string is extracted.

void close();

Close file

Closes the file currently associated with the object, disassociating it from the stream.

Any pending output sequence is written to the file.

If the stream is currently not associated with any file (i.e., no file has successfully been open with it), calling this function fails.

the failbit state flag is set for the stream (which may throw ios_base::failure if that state flag was registered using member exceptions).