The usage of getline()

Question

_{Monday, August 21, 2017 6:24 AM}

My codes are similar to below snippet. I got error of "...error C3861: 'getline': identifier not found ...".

If I added #include <iostream> and change getline() as std::getline(), I got error:

"'std::getline': no matching overloaded function found".
'std::basic_istream<_Elem,_Traits> &std::getline(std::basic_istream<_Elem,_Traits> &,std::basic_string<_Elem,_Traits,_Alloc> &)': expects 2 arguments - 3 provided

How should I use getline() correctly? My platform is VS2015.

#include <stdio.h>
#include <stdlib.h> 

    ``FILE`` *file = ``fopen``(filename, ``"r"``);

 .....

    ``// read each line and print it to the screen
    ``int`` line_number = ``0``;
    ``while``(``-1`` != ``getline``(&buffer, &buffer_size, file))
    {
        ``printf``(``"``%d``: ``%s``"``, ++line_number, buffer);
    }

All replies (7)

_{Monday, August 21, 2017 7:39 AM ✅Answered | 1 vote}

Hello,

use the std-lib like this:

#include <fstream>

CString szFilename = _T(" <your filename> ");
std::ifstream fi;
fi.open((LPCTSTR)szFilename);
if (!fi.is_open())
{
   return;
}

char szline[10240];
while (fi.getline(szline, 10240))
{
   // ...
}
fi.close();

Regards, Guido

_{Monday, August 21, 2017 11:34 AM ✅Answered | 1 vote}

On 8/21/2017 2:24 AM, Stan Huang at Taiwan wrote:

    FILE *file = fopen(filename, "r");

std::getline is designed to read from std::istream or a class derived therefrom; not from FILE*. And it reads into std::string, not a raw buffer. If you insist on using FILE* and raw buffer, there's fread(). Otherwise:

std::ifstream file(filename);
std::string line;
int line_number = 0;
while (std::getline(file, line)) {
    std::cout << ++line_number << ": " << line;
}

_{Monday, August 21, 2017 7:18 PM ✅Answered | 1 vote}

How should I use getline() correctly? My platform is VS2015.

#include <stdio.h>
#include <stdlib.h> 

    ``FILE`` *file = ``fopen``(filename, ``"r"``);

 .....

    ``// read each line and print it to the screen
    ``int`` line_number = ``0``;
    ``while``(``-1`` != ``getline``(&buffer, &buffer_size, file))
    {
        ``printf``(``"``%d``: ``%s``"``, ++line_number, buffer);
    }

By way of fleshing out some of the details, take note that there are
two getline() functions:

(1) istream::getline
https://msdn.microsoft.com/en-us/library/aa277361(v=vs.60).aspx

This is a member function of basic_istrean and its derivatives.
It reads the string into a "raw" or "native" character array.
The reply from Guido uses this version of getline.

(2) std::getline (from <string>)

https://msdn.microsoft.com/en-CA/library/2whx1zkx(v=vs.100).aspx
https://msdn.microsoft.com/library/1a4ffd11-dce5-4cc6-a043-b95de034c7c4.aspx#getline_template_function

Unlike (1) above, this is not a member function of a class.
It reads the string into a std::string.
The reply from Igor uses this version of getline.

As noted by Igor, if you must use the input streams from the C Standard
Library (fopen, FILE*) then the preferred route would be to use the
functions provided for manipulating such streams. To read strings, see:

fgets, fgetws
https://msdn.microsoft.com/en-us/library/c37dh6kf.aspx

• Wayne

_{Tuesday, August 22, 2017 3:39 AM ✅Answered | 1 vote}

On 8/21/2017 11:33 PM, Stan Huang at Taiwan wrote:

It works basically. But why the line "

<p>std::cout << ++line_number << <span style="margin:0px; padding:0px; border:0px; vertical-align:baseline; color:#a31515">": "</span> << line;"</p><p></p><p>I got error of</p>

"error C2039: 'cout': is not a member of 'std'"

You are probably missing #include <iostream>

_{Tuesday, August 22, 2017 5:13 AM ✅Answered | 1 vote}

I learned the usage of getline() form http://timmurphy.org/2010/10/31/reading-from-a-file-in-c-2/

I guessed it worked at some situation. So, how come it doesn't work at VS environment?

That uses a non-standard C extension that is supported by some compilers
on some platforms. It is not part of the ISO C99 Standard nor the ISO
C++ Standard, and is not supported by Visual C++. See:

undefined reference to `getline' in c
https://stackoverflow.com/questions/13112784/undefined-reference-to-getline-in-c

• Wayne

_{Tuesday, August 22, 2017 3:33 AM}

It works basically. But why the line "

<p>std::cout << ++line_number << <span style="margin:0px; padding:0px; border:0px; vertical-align:baseline; color:#a31515">": "</span> << line;"</p><p></p><p>I got error of</p>

"error C2039: 'cout': is not a member of 'std'"

_{Tuesday, August 22, 2017 4:21 AM}

I learned the usage of getline() form http://timmurphy.org/2010/10/31/reading-from-a-file-in-c-2/

I guessed it worked at some situation. So, how come it doesn't work at VS environment?