How to read specific first character and save the data by C++

Question

I am the newbie of C++.

I want to write a program that can read the file such lik below:

p   6   9
n   3
b   1   6.0
b   1   4.0
b   2   2.0

In such file, I want to read the line with first char b.
I try to use getline() and to judge whether the first char is b.
However, I face the problem is I can easily save the first int, but the second double number I can't save it. I know the reason is I save it in char, so the dobule number are seperated(such like 6.0 become '6' '.' '0').
Thus, does it have other way to save the line with integer and double?

#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main(){

    char b[100];
    string word;
    int a,d;
    double c;
    ifstream infile("test.txt");
    while(infile){
        infile.getline(b,100);
        if(b[0] == 'b'){
            //where I don't know how to save the data
        }
    }
}

I'm sorry for my rusty English, but really need your help.

You might want to read about std::istringstream. With it you can use the normal input operator >>. — Some programmer dude
– Some programmer dude, Commented Feb 19, 2014 at 17:43

herohuyongtao · Accepted Answer · 2014-02-19 18:00:39Z

2

Just put the whole string into a std::istringstream and use >> to get its data out:

int int_value;      // second data will be saved here, e.g. 1
float float_value;  // third data will be saved here, e.g. 6.0

char char_dummy;    // dummy char to hold the first char, e.g. 'b'
istringstream iss(b);
iss >> char_dummy >> int_value >> float_value;

edited Feb 19, 2014 at 18:00

answered Feb 19, 2014 at 17:43

herohuyongtao

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1 Comment

MattD Over a year ago

Since you control the format of the data, solutions like istringstream are your friend. It is very clean and less error-prone than older C-style solutions like fscanf, etc.

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