C++ Read File with multiple column

Question

I'd like to read a file with multiple columns, different variable types. The number of columns is uncertain, but between 2 or four. So for instance, I have a file with :

string int

string int string double

string int string

string int string double

Thanks!

I edited to correct the number of columns to between 2 or 5, not 4 or five as originally written.

So you want us to write you code? You're not paying us? So please do research and ask questions here about specific problems you encounter along the way. — Tony The Lion
– Tony The Lion, Commented Mar 4, 2013 at 16:45
How are the columns divided? If with whitespace (space or tab) then the normal input operator >> will work fine. — Some programmer dude
– Some programmer dude, Commented Mar 4, 2013 at 16:45
The number of columns is uncertain, but between 4 or five --- yet your example shows that the first row only contains 2 columns, and not a single one contains 5 columns! — Praetorian
– Praetorian, Commented Mar 4, 2013 at 16:47
1) read a line. 2) tokenize it somehow. 3) come back if you have a real question. — Useless
– Useless, Commented Mar 4, 2013 at 17:40

Olaf Dietsche · Accepted Answer · 2013-03-04 16:51:10Z

5

You can first read the line with std::getline

std::ifstream f("file.txt");
std::string line;
while (std::getline(f, line)) {
...
}

and then parse this line with a stringstream

std::string col1, col3;
int col2;
double col4;
std::istringstream ss(line);
ss >> col1 >> col2;
if (ss >> col3) {
    // process column 3
    if (ss >> col4) {
        // process column 4
    }
}

If the columns might contain different types, you must first read into a string and then try to determine the proper type.

answered Mar 4, 2013 at 16:51

Olaf Dietsche

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1 Comment

Marcel Over a year ago

Don't forget #include <sstream>

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