Why first getline doesnt work?

This is a discussion on Why first getline doesnt work? within the C++ Programming forums, part of the General Programming Boards category; I have written a program, which is supposed to read 3 lines from a text file, the first is char, ...

  1. #1
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    Why first getline doesnt work?

    I have written a program, which is supposed to read 3 lines from a text file, the first is char, second string and thirs an integer. The input.txt is:
    Code:
    i
    Arnold Schwarzenegger
    60
    And my code:
    Code:
    int main()
    {
    	ifstream data("input.txt");
    	string name;
    	int age;
    	char instr;
    
    	data >> instr;
    	getline(data, name);
    	data >> age;
    }
    However, the getline does not read anything from the file, and after that, when the program processes to the next line of code, the 'data >> age' statement tries to read the 'Arnold Schwarzenegger' field into the age variable...
    Why is that? Why does the getline read nothing? How do I make it work?

  2. #2
    and the hat of wrongness Salem's Avatar
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    Getline is reading the newline after the i, since all you're doing with the first >> is reading a single character.

    You're generally better off reading each line (using getline) into a buffer, then parsing that buffer to see what it contains.

    Mixing and matching input styles is always a bug at some point.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  3. #3
    printf("Hello Cboard\n"); codeprada's Avatar
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    have a call to the ignore function before your getline so that the '\n' from the previous line won't be parsed by the getline function causing it to read nothing and thus throwing off your data >> age line

    Code:
    #include <iostream>
    #include <fstream>
    
    using namespace std;
    
    int main(int argc, char * argv[])
    {
    	ifstream data("read.txt");
    	char * name = new char[256]; //same as char name[256]
    	int age;
    	char instr;
        if(data.is_open()){
            data >> instr;
            data.ignore(1, '\n');
            data.getline(name, 256, '\n');
            data >> age;
            cout << "instr -> " << instr
                 << endl << "name -> " << name
                 << endl << "age -> " << age;
        }
        else
            cout << "could not open file";
    
        cin.get();
        return 0;
    }
    We shouldn't be quick to criticize unless we can do better.
    Code:
    public function __clone() { die ( "I'm one of a kind" ); }

  4. #4
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by codeprada View Post
    have a call to the ignore function before your getline so that the '\n' from the previous line won't be parsed by the getline function causing it to read nothing and thus throwing off your data >> age line
    Gah! All C with some convenient C++ stuff mixed in. Let's fix this.

    Code:
    #include <iostream>
    #include <fstream>
    
    using namespace std;
    
    int main(int argc, char * argv[])
    {
    	ifstream data("read.txt");
    	std::string name;
    	int age;
    	char instr;
        if(data.is_open()){
            data >> instr;
            data.ignore(1, '\n');
            getline(name, cin);
            data >> age;
            cout << "instr -> " << instr
                 << endl << "name -> " << name
                 << endl << "age -> " << age;
        }
        else
            cout << "could not open file";
    
        cin.get();
        return 0;
    }
    This is better. Though it still doesn't handle invalid input.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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