C++ - Extract string from comma separated float line

Question

I have a file with the following pattern: 0.123,0.432,0.123,ABC

I've successfully retrieved the float numbers to an array, but I need now to find a way to get the last string. My code is the following:

    vector<float> test;
    for (float v = 0; test_ss >> v; ) {
        test.push_back(v);
        test_ss.ignore();
    }

Tips:

As the number of elements in each line is known its not a problem
Also I don't particularly need to use this structure, I was just using it because it was the best I've found so far.
All I want is in the end to have a vector with the float elements and a string with that last field.

no i need only the string, but i'm new at c++ and i don't know how to do it using c++ (this is an requirement) — Gregório Granado Magalhães, Dec 15 '17 at 20:19
It seems you want to get the substring after the last `,`. A regex for this can be `[^,]+$`. — Wiktor Stribiżew, Dec 15 '17 at 20:20
@GregórioGranadoMagalhães `std::regex` seems overkill to parse that. — user0042, Dec 15 '17 at 20:29
The easiest approach is to read the known number of floats followed by reading the string: what exactly is your problem with doing so? Alternatively, read the line, find the last comma, and use the string starting after that (if it may contain commas just find the *n*th comma). — Dietmar Kühl, Dec 15 '17 at 20:37
Yes, it's the easiest, but since it's an academic homework I think a more "advanced" approach would be "smarter" but if in the end I can't find another way that's what I'm going to do — Gregório Granado Magalhães, Dec 15 '17 at 20:43
I'm trying the following but it doesn't work: https://ideone.com/PSVo6X — Gregório Granado Magalhães, Dec 15 '17 at 20:56
Use [`s.substr(s.find_last_of(",") + 1)`](https://ideone.com/MxlAT7) — Wiktor Stribiżew, Dec 15 '17 at 20:56
@WiktorStribiżew `s.substr(s.find_last_of(",") + 1)` worked thanks. — Gregório Granado Magalhães, Dec 15 '17 at 20:59

score 0 · Answer 1 · answered Dec 15 '17 at 21:03

0

A simple solution would be to first replace the string using std::replace( test_ss.begin(), test_ss.end(), ',', ' '); then to use your for loop:

vector<float> test;
for (float v = 0; test_ss >> v; ) {
    test.push_back(v);
    test_ss.ignore();
}

answered Dec 15 '17 at 21:03

Jake Freeman

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Killzone Kid · Answer 2 · 2017-12-15T21:15:19.520

RegEx would be an overkill for this task, and substr will return string while you asked for float vector. I think what you need is to use ifstream and read comma into a dummy char:

#include <iostream>
#include <vector>
#include <string>
#include <fstream>

int main() 
{
    std::ifstream ifs("file.txt");

    std::vector<float> v(3);
    std::string s;
    char comma; // dummy

    if (ifs >> v[0] >> comma >> v[1] >> comma >> v[2] >> comma >> s)
    {
        for (auto i : v)
            std::cout << i << " -> ";

        std::cout << s << std::endl;
    }

    return 0;
}

Prints:

0.123 -> 0.432 -> 0.123 -> ABC

C++ - Extract string from comma separated float line

2 Answers2