Differences

This shows you the differences between two versions of the page.

--- cplusplus:file_processing_examples [2013/03/01 01:07] – mithat
+++ cplusplus:file_processing_examples [2019/02/11 19:17] (current) – [Using filenames] mithat
@@ Line 2: / Line 2: @@
 ===== File writing =====
+==== Simple example ====
+<file c++ simple-file-write.cpp>// This program writes data to a file.
+#include <iostream>
+#include <fstream>
+using namespace std;
+int main()
+{
+    ofstream outfile;   // instantiate file pointer object
+    outfile.open("public_radio.txt");   // associate file with file pointer object
+    cout << "Writing to the file ... ";
+    outfile << "KCMP\t" << 89.3 << endl;
+    outfile << "KNOW\t" << 91.1 << endl;
+    outfile << "KSJN\t" << 99.5 << endl;
+    outfile.close();    // close the file!
+    cout << "Done!" << endl;
+    return 0;
+}
+</file>
+==== Checking for opening errors ====
+<file c++ simple-file-write2.cpp>// This program writes data to a file.
+// Shows error checking.
+#include <iostream>
+#include <fstream>
+using namespace std;
+int main()
+{
+    ofstream outfile;   // instantiate file pointer object
+    outfile.open("public_radio.txt");   // associate file with file pointer object
+    if (!outfile)
+    {
+        cout << "Error opening file." << endl;
+        return 1;  // exit program with an error code
+    }
+    cout << "Writing to the file ... ";
+    outfile << "KCMP\t" << 89.3 << endl;
+    outfile << "KNOW\t" << 91.1 << endl;
+    outfile << "KSJN\t" << 99.5 << endl;
+    outfile.close();    // close the file!
+    cout << "Done!" << endl;
+    return 0;
+}
+</file>
+==== Using filenames ====
+<file c++ simple-file-write3.cpp>// This program writes data to a file.
+// Converting string to c_str.
+#include <iostream>
+#include <fstream>
+#include <cstring>
+using namespace std;
+int main()
+{
+    ofstream outfile;   // instantiate file pointer object
+    string filename;    // used to store filename to save file
+    // get filename from user
+    cout << "Enter the filename to store the file in\n"
+         << "> ";
+    cin >> filename;
+    outfile.open(filename);            // associate file with file pointer object
+    //outfile.open(filename.c_str());  // convert filename to C-string in pre-C++11
+    if (!outfile)
+    {
+        cout << "Error opening file." << endl;
+        return 1;  // exit program with an error code
+    }
+    cout << "Writing to the file ... ";
+    outfile << "KCMP\t" << 89.3 << endl;
+    outfile << "KNOW\t" << 91.1 << endl;
+    outfile << "KSJN\t" << 99.5 << endl;
+    outfile.close();    // close the file!
+    cout << "Done!" << endl;
+    return 0;
+}
+</file>
 ===== File reading =====
+==== Simple example ====
+<file c++ simple-file-read.cpp>// This program reads a number from a file.
+#include <iostream>
+#include <fstream>
+#include <string>
+using namespace std;
+int main()
+{
+    string filename = "some_numbers.txt";
+    int num1;
+    ifstream infile;         // instantiate file pointer object
+    infile.open(filename);   // associate file with file pointer object
+    if (!infile)
+    {
+        cout << "Error opening file." << endl;
+        return 1;  // exit program with error code
+    }
+    cout << "Reading from file ... ";
+    infile >> num1;
+    infile.close();    // close the file!
+    cout << "Done!" << endl;
+    cout << "The first number in the file is " << num1 << "." << endl;
+    return 0;
+}
+</file>
+==== Reading multiple tokens ====
+<file c++ simple-file-read2.cpp>// This program reads two numbers from a file.
+#include <iostream>
+#include <fstream>
+#include <string>
+using namespace std;
+int main()
+{
+    string filename = "some_numbers.txt";
+    int num1, num2;
+    ifstream infile;         // instantiate file pointer object
+    infile.open(filename);   // associate file with file pointer object
+    if (!infile)
+    {
+        cout << "Error opening file." << endl;
+        return 1;  // exit program with error code
+    }
+    cout << "Reading from file ... ";
+    infile >> num1 >> num2;
+    infile.close();    // close the file!
+    cout << "Done!" << endl;
+    cout << "The first two numbers in the file are:" << endl
+         << num1 << endl
+         << num2 << endl
+         << endl;
+    return 0;
+}
+</file>
+==== Read all tokens in a file ====
+<file c++ simple-file-read3.cpp>// This program reads all the numbers from a file.
+#include <iostream>
+#include <fstream>
+#include <string>
+using namespace std;
+int main()
+{
+    const string filename = "some_numbers.txt";
+    int num1;
+    ifstream infile;         // instantiate file pointer object
+    infile.open(filename);   // associate file with file pointer object
+    if (!infile)
+    {
+        cout << "Error opening file." << endl;
+        return 1;  // exit program with error code
+    }
+    cout << "Reading from file ... " << endl;
+    while (infile >> num1)
+    {
+        cout << num1 << endl;
+    }
+    infile.close();    // close the file!
+    cout << "Done!" << endl;
+    return 0;
+}
+</file>