Using getline() with file input in C++

Question

I am trying to do a simple beginner's task in C++. I have a text file containing the line "John Smith 31". That's it. I want to read in this data using an ifstream variable. But I want to read the name "John Smith" into one string variable, and then the number "31" into a separate int variable.

I tried using the getline function, as follows:

ifstream inFile;
string name;
int age;

inFile.open("file.txt");

getline(inFile, name); 
inFile >> age; 

cout << name << endl;
cout << age << endl;  

inFile.close();

The problem with this is that it outputs the entire line "John Smith 31". Is there a way I can tell the getline function to stop after it has gotten the name and then kind of "restart" to retrieve the number? Without manipulating the input file, that is?

If you don't want to read a line, don't call getline. It really is that simple. — David Schwartz
– David Schwartz, Commented Dec 23, 2013 at 8:16

Johan · Accepted Answer · 2013-12-23 08:19:39Z

15

getline, as it name states, read a whole line, or at least till a delimiter that can be specified.

So the answer is "no", getlinedoes not match your need.

But you can do something like:

inFile >> first_name >> last_name >> age;
name = first_name + " " + last_name;

answered Dec 23, 2013 at 8:19

Johan

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2 Comments

Zeeshan Over a year ago

I meant, if it works this way. I read somewhere, we need to specify string as std::string x;, to use + for concatination. otherwise, compiler assumes that you are trying to add char pointers. is that rite? or it just works the way mentioned? just wanted to make clear, for myself. Thank you

Johan Over a year ago

If you look at the list of overload of operator+() with a std::string you'll see that it works as soon as on of the parameter is a std::string. No magic there :) But it you call + with to char* it won't work.

user153245 · Accepted Answer · 2020-07-09 10:26:55Z

7

ifstream inFile;
string name, temp;
int age;

inFile.open("file.txt");

getline(inFile, name, ' '); // use ' ' as separator, default is '\n' (newline). Now name is "John".
getline(inFile, temp, ' '); // Now temp is "Smith"
name.append(1,' ');
name += temp;
inFile >> age; 

cout << name << endl;
cout << age << endl;  

inFile.close();

edited Jul 9, 2020 at 10:26

user153245

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answered Dec 23, 2013 at 8:32

SliceSort

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Comments

Zeeshan · Accepted Answer · 2013-12-23 08:26:02Z

3

you should do as:

getline(name, sizeofname, '\n');
strtok(name, " ");

This will give you the "joht" in name then to get next token,

temp = strtok(NULL, " ");

temp will get "smith" in it. then you should use string concatination to append the temp at end of name. as:

strcat(name, temp);

(you may also append space first, to obtain a space in between).

answered Dec 23, 2013 at 8:26

Zeeshan

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1 Comment

Shipof123 Over a year ago

strtok() is more of a C solution. It might be better to introduce new users into STL concepts

maher alaqil · Accepted Answer · 2020-11-20 16:00:07Z

-1

you can use getline from a file using this code. this code will take a whole line from the file. and then you can use a while loop to go all lines while (ins);

 ifstream ins(filename);
string s;
std::getline (ins,s);

answered Nov 20, 2020 at 16:00

maher alaqil

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1 Comment

Sylvaus Over a year ago

This does not seem to answer the question, try to add more information to properly answer the question

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