Taking string objects using getline

Question

I am trying to take user input directly from console using getline into a C++ string object. I am however failing to do so as the compiler gives me the following error.

main.cpp: In function ‘int main(int, char**)’:
main.cpp:52:28: error: no matching function for call to ‘std::basic_ifstream<char>::getline(std::ifstream&, std::string&)’
main.cpp:52:28: note: candidates are:
/usr/include/c++/4.6/istream:599:5: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::getline(std::basic_istream<_CharT, _Traits>::char_type*, std::streamsize, std::basic_istream<_CharT, _Traits>::char_type) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::char_type = char, std::streamsize = int]
/usr/include/c++/4.6/istream:599:5: note:   candidate expects 3 arguments, 2 provided
/usr/include/c++/4.6/istream:408:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::getline(std::basic_istream<_CharT, _Traits>::char_type*, std::streamsize) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>, std::basic_istream<_CharT, _Traits>::char_type = char, std::streamsize = int]
/usr/include/c++/4.6/istream:408:7: note:   no known conversion for argument 2 from ‘std::string {aka std::basic_string<char>}’ to ‘int’

Here is the source code:

#include <iostream>
 #include <fstream>
 #include <cmath>
 #include <cstdlib>
 #include <cstring>
 #include <string>
 #include <map>
 #include <set>
 #include <algorithm>
 #include <cstdio>

 #define MAX_LIN 1024

 using namespace std;

 typedef set<int> si;
int main(int argc, char** argv)
 {   
     string line1;
     string line2;

     map <string , si > iMap;

     if (argc != 3) { 
         fprintf(stderr,"Usage: a.out <file1> <file2>\n");
     }

     ifstream f1,f2;

     f1.open(argv[1],ifstream::in);
     f2.open(argv[2],ifstream::in);

     while(!f1.eof()) {
         getline(f1,line1);
         mParse(line1);
     }   

     while(!f2.eof()) {
         f2.getline(f2,line2);
         mParse(line2);
     }   

     f1.close();
     f2.close();


     return 0;
 }

Did you #include <string>? Please add your include directives to the posted code, I don't see any. — hmjd
– hmjd, Commented Oct 6, 2012 at 12:59
@humanitarian0098: It is a good idea to learn to read compiler messages. They are not always the prettiest, but we do have to deal with them on a daily basis after all. std::basic_ifstream<char>::getline(std::ifstream&, std::string&) can also be seen as std::ifstream::getline(std::ifstream&, std::string&), this is the compiler guessing what you were trying to call. Note how it indicates both that: 1/ it is a method of std::ifstream that you were calling and 2/ you passed std::ifstream& and std::string& as parameters. — Matthieu M.
– Matthieu M., Commented Oct 6, 2012 at 14:27

hmjd · Accepted Answer · 2012-10-06 13:01:06Z

6

This is the cause:

f2.getline(f2,line2);

should be:

getline(f2,line2);

There is a std::ifstream::getline() but it accepts different arguments.

Note the structure of the while loops is incorrect as eof() should be checked immediately after a read operation. A common way of coding the loop is:

while (getline(f2, line2))
{
    mParse(line2);
}

answered Oct 6, 2012 at 13:01

hmjd

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Comments

Kerrek SB · Accepted Answer · 2012-10-06 13:01:20Z

0

Here's the canonical way:

 std::ifstream f1(argv[1]);
 std::ifstream f2(argv[2]);

 for (std::string line; std::getline(f1, line); )
 {
     mparse(line);
 }

 for (std::string line; std::getline(f2, line); )
 {
     mparse(line);
 }

Note everything we don't write, each of which should be considered a capital sin: eof, open, close, ifstream::in, return 0.

answered Oct 6, 2012 at 13:01

Kerrek SB

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