C++ : How to skip first whitespace while using getline() with ifstream object to read a line from a file?

Question

I have a file named "items.dat" with following contents in the order itemID, itemPrice and itemName.

item0001 500.00 item1 name1 with spaces
item0002 500.00 item2 name2 with spaces
item0003 500.00 item3 name3 with spaces

I wrote the following code to read the data and store it in a struct.

#include <fstream>
#include <iostream>
#include <string>
#include <cstdlib>
#include <iomanip>

using namespace std;

struct item {
    string name;
    string code;
    double price;
};

item items[10];

void initializeItem(item tmpItem[], string dataFile);

int main() {

    initializeItem(items, "items.dat");
    cout << items[0].name << endl;
    cout << items[0].name.at(1) << endl;
    return 0;
}

void initializeItem(item tmpItem[], string dataFile) {

    ifstream fileRead(dataFile);

    if (!fileRead) {
        cout << "ERROR: Could not read file " << dataFile << endl;
    }
    else {
        int i = 0;
        while (fileRead >> tmpItem[i].code) {
            fileRead >> tmpItem[i].price;
            getline(fileRead, tmpItem[i].name);
            i++;
        }
    }
}

What I notice is the getline() reads the white space at the beginning while reading item name along with the content.

Output

 name1 with spaces
n

I want to skip the whitespace at the beginning. How can I do that?

Instead of skipping the white-space, why not trim the string after reading? — Some programmer dude
– Some programmer dude, Commented Jul 26, 2017 at 9:06
But we will have to write a trim function by ourselves, right? — Anj Jo
– Anj Jo, Commented Jul 26, 2017 at 9:13
Yes, but it's easy and there are many examples all over the 'net (including quite a few here on SO). — Some programmer dude
– Some programmer dude, Commented Jul 26, 2017 at 9:13

Blastfurnace · Accepted Answer · 2017-07-26 09:13:23Z

7

The std::ws IO manipulator can be used to discard leading whitespace.

A compact way to use it is:

getline(fileRead >> std::ws, tmpItem[i].name);

This discards any whitespace from the ifstream before it's passed to getline.

answered Jul 26, 2017 at 9:13

Blastfurnace

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5 Comments

Anj Jo Over a year ago

This worked. BTW does this work for trailing whitespaces too?

Blastfurnace Over a year ago

@AnjJo Are you talking about your getline call? Unfortunately getline reads the entire line until the default delimiter (a newline) or EOF. If there are trailing spaces you'll need to trim them.

Anj Jo Over a year ago

How can i use std::ws to trim trailing whitespace?

Blastfurnace Over a year ago

@AnjJo In combination with getline? You can't, that reads everything up to but not including the newline. You'll need to use some string trimming code (search here on SO). std::ws is most useful in discarding whitespace left from a previous stream extraction (>>) operation.

Blastfurnace Over a year ago

@AnjJo This may help: What's the best way to trim std::string?

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