Read Numeric Data from a Text File in C++

Read Numeric Data from a Text File in C++

Repeat >> reads in loop.

#include <iostream>
#include <fstream>
int main(int argc, char * argv[])
{
    std::fstream myfile("D:\\data.txt", std::ios_base::in);

    float a;
    while (myfile >> a)
    {
        printf("%f ", a);
    }

    getchar();

    return 0;
}

Result:

45.779999 67.900002 87.000000 34.889999 346.000000 0.980000

If you know exactly, how many elements there are in a file, you can chain >> operator:

int main(int argc, char * argv[])
{
    std::fstream myfile("D:\\data.txt", std::ios_base::in);

    float a, b, c, d, e, f;

    myfile >> a >> b >> c >> d >> e >> f;

    printf("%f\t%f\t%f\t%f\t%f\t%f\n", a, b, c, d, e, f);

    getchar();

    return 0;
}

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Edit: In response to your comments in main question.

You have two options.

• You can run previous code in a loop (or two loops) and throw away a defined number of values - for example, if you need the value at point (97, 60), you have to skip 5996 (= 60 * 100 + 96) values and use the last one. This will work if you're interested only in specified value.
• You can load the data into an array - as Jerry Coffin sugested. He already gave you quite nice class, which will solve the problem. Alternatively, you can use simple array to store the data.

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Edit: How to skip values in file

To choose the 1234th value, use the following code:

int skipped = 1233;
for (int i = 0; i < skipped; i++)
{
    float tmp;
    myfile >> tmp;
}
myfile >> value;

C Reading Numbers From Text File

You need to seek to the beginning of the file after counting all the commas. You're at the end of the file when you start the fscanf() loop, so they're all failing and you're not reading anything.

The loop that reads the numbers should only run counter times. res is the number of bytes in the file, which is at least twice as many numbers. There's no point in using res.

#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <ctype.h>

int main() {
    FILE *file;
    file = fopen("example_input.txt","r");
    int m;
    int counter = 0;
    while((m = fgetc(file)) != EOF) {
        if (m == ',') {
            counter++;
        }
    }
    counter++; // 1 more for the last number
    int n[counter] = {0};

    fseek(file, 0L, SEEK_SET);

    for (int i = 0; i < counter; i++) {   
        if (fscanf(file, "%d,", &n[i]) != 1) {
            break;
        }
    }
    for (int a = 0; a < counter; a++) {
        printf("%d ", n[a]);
    }
} 

Reading numbers from a text file into an array in C

change to

fscanf(myFile, "%1d", &numberArray[i]);

Reading multiple numbers from a text file in C

It's better if you don't use a loop with a hardcoded number limit. In my solution I read the numbers until there aren't any numbers left. You'll also not want to use a return statement inside your loop as that will exit the current function.

#include <stdio.h>
#include <limits.h>

int main()
{
    int smallest = INT_MAX;
    int second_smallest = INT_MAX;
    int number;

    FILE *infile = fopen("numbers.txt", "r");
    if (infile)
    {
        while (fscanf(infile, "%d", &number) == 1)
        {
            if (number < smallest)
            {
                second_smallest = smallest;
                smallest = number;
            }
            else if (number < second_smallest)
            {
                second_smallest = number;
            }
        }
        fclose(infile);
    }

    printf("smallest: %d\n", smallest);
    printf("second smallest: %d\n", second_smallest);
    return 0;
}

Reading integer to a text file in C (integer is present in a structure)

I guess you are trying to read the file using a text editor.

Issue is with fwrite:
"fwrite" will write the numbers without converting it to ASCII or utf-8 chars hence numbers won't be found when opened via file editor. Instead, you will find a characters equivalent of the numbers stored. Try reading the file using "fread" you will get the actual values back into the "employee_details" structure.

Incase you want to read the data via file editor: use fprint

Try something Like:
fprintf(p_wfile , "%s %d\n", employee.name, employee.id);

How to read a number from a file and use it as a variable in C++?

Hope this piece of code will help.

#include <bits/stdc++.h>
using namespace  std;         //change headers and namespaces; included for ease of use;

vector<string> split(const string &text, const char sep) {
    vector<string> tokens;
    std::size_t start = 0, end = 0;
    while ((end = text.find(sep, start)) not_eq string::npos) {
        tokens.emplace_back(text.substr(start, end - start));
        start = end + 1;
    }
    tokens.emplace_back(text.substr(start));
    return tokens;
}

    int main()
    {
       ofstream outdata;
       outdata.open("example.txt");
       if( not outdata ) {
          cerr << "Error: file could not be opened" << endl;
          exit(1);
       }
       outdata<<"CharacterName1"<<','<<10.0<<','<<40.0<<endl; //writing data into file
       outdata<<"CharacterName2"<<','<<20.0<<','<<30.0<<endl;
       outdata<<"CharacterName3"<<','<<30.0<<','<<20.0<<endl;
       outdata<<"CharacterName4"<<','<<40.0<<','<<10.0<<endl;
       outdata.close();

        ifstream inputFile;
        inputFile.open("example.txt",fstream::in);
        if (inputFile.fail())
        {
            cerr<<"Error: file could not be opened"<<endl;
            exit(1);
        }
        string line;
        vector<string> col1;
        vector<double> col2;
        vector<double> col3;
        while (getline(inputFile, line))
        {
            if(not line.empty()){

            auto lineData = split(line, ','); //separator can change in your case
            col1.emplace_back(lineData[0]);
            col2.emplace_back(std::stof(lineData[1]));
            col3.emplace_back(std::stof(lineData[2]));
            }
        }
        for(int i =0; i<(int) col1.size();i++)         //printing the data;
            cout<<col1[i]<<"\t"<<col2[i]<<"\t"<<col3[i]<<"\n";
       return 0;
    }

understand the above logic through the following approach:

1. read each line of the file.

2. for each line we will separate the column data through the split(string, sep) function which will return a vector<string> containing data of the row. Here sep is the separator used in the file; as I made input file comma-separated, I used ','

3. converting the returned vector<string> type row-data into appropriate data type and storing in respective column vector col1, col2, col3.

4. reference of split() functionality.

for another column that may have some missing data
you can add some logic like

if(lineData.size() > 3)
    col4.emplace_back(std::stof(lineData[3]));
else
    col4.emplace_back(0.0);

after col3.emplace_back(std::stof(lineData[2])); line.

(c++) Reading numeric data in a column from a txt file and determining highest value

If you have the option of using the file as an input, then you could use simple cin in order to get your values for Time,Volt and Amp. ( the only thing you need to keep in mind is to ignore first row because they are just names)

If you know that all three values in each row will be present, then you can create while loop that runs until EOF. Then you read 3 values (Time, Volt, Amp) and compare with the previous Volt.
If previous volt is larger - ignore this row and move on.
Else - keep current Time, Volt and Amp.

On the next iteration, compare new 3 values to the max value of Volt so far.

Here is my "quick and dirty" solution:

#include <iostream>
#include <string>
using namespace std;

int main()
{
// cin>>temp goes through names and ignores it since we don't need it
string temp;
cin >> temp;
cin >> temp;
cin >> temp;

float timeval = 0;
float volt = 0;
float amp = 0;
float timevalTemp = 0;
float voltTemp = 0;
float ampTemp = 0;

while(cin >> timevalTemp >> voltTemp >> ampTemp)
{
    if(voltTemp > volt)
    {
        timeval = timevalTemp;
        volt = voltTemp;
        amp = ampTemp;
    }
}
cout << "Max Time: " << timeval << endl;
cout << "Max Volt: " << volt << endl;
cout << "Max Amp: "<< amp << endl;
return 0;
}

Let me know if something is not clear. I ran it on your text file and it produces:

Max Time: 0.00035
Max Volt: 9.78167
Max Amp: 0.1473

Reading numbers from a text file with letters and whitespace

Assuming that your goal is not to retain the accuracy of the double values in the file, one way to do this is to read the line in as a string, and remove any characters that are not digits, except whitespace and the ..

Once you do that, then it's very simple using std::istringstream to output the values:

#include <iostream>
#include <string>
#include <sstream>
#include <algorithm>
#include <cctype>

int main()
{
    std::string line;
    // Read the entire line
    while (std::getline(std::cin, line))
    {
        // erase all non-digits, except for whitespace and the '.' 
        line.erase(std::remove_if(line.begin(), line.end(), 
                   [](char ch) { return !std::isdigit(ch) && !std::isspace(ch) && ch != '.'; }), line.end());

        // Now use the resulting line and read in the values
        std::istringstream strm(line);
        double oneValue;
        while (strm >> oneValue)
           std::cout << oneValue << " ";
    }
}

Output:

87 98.5 4 9 0 94.3 98.4 84 

Live Example

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