Incorrectly reading .dat file in c++

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I am new to c++ and have gotten to a module about file i/o. I have copied the example from my textbook verbatim and it does not seem to work as expected and I am not sure what the problem could be; there are no errors that are output from the program.

I have tried different variations and settled on this example:

#include <fstream>
#include <iostream>

using namespace std;

string f = "marks.dat"; ifstream file;


int main() {
    int first = 0;
    file.open(f);
    if(file.is_open()){
        file >> first;
        cout << first;
    } else {
    cout << "file has failed to open";
    }

    return 0;
}

The .dat file is in the folder Assignment3.1 from which the .cpp file is compiled. The check for "file.is_open()" is false and I am not sure what the issue is.

The output of my code is as follows: Output

EDIT: I have included a declaration for first = 0; and included a file.is_open();

EDIT: the pwd for the folder is: /Users/stjohn/Documents/cpp/Assignment3.1

I think file is not being read properly. You are getting random number from variable first. Try to initialise first to zero and then see output. You should understand what is going on.

first=0;

DAT file reading in C, please post the code that writes the file. line 18: why is the loop hardcoded with that magic number instead of using the int that was previously  When the file is closed: before closing a file, all buffers that have not yet been flushed are synchronized and all pending data is written or read to the physical medium. When the buffer is full: Buffers have a certain size. When the buffer is full it is automatically synchronized. Explicitly,

The current file is not being read because it is not contained within the correct directory from which the program executes. By using the full file path in the string declaration the program will be able to read the file.

#include <fstream>
#include <iostream>

using namespace std;

string f = "/Users/stjohn/Documents/cpp/Assignment3.1/marks.dat"; ifstream file;


int main() {
    int first = 0;
    file.open(f);
    if(file.is_open()){
        file >> first;
        cout << first;
    } else {
    cout << "file has failed to open";
    }

    return 0;
}

Read .dat file - C++ Forum, How can I read the generated file in C ? 9,4,2,9,5,9,9,6,6}; int main ( int argc, char **argv) { FILE *fp; fp = fopen ( "Test.dat" , "wb" ); fwrite (arr, 3, 44, fp); fclose (​fp); }. Edit & Run Your second parameter to fwrite is wrong. This function actually flushes any data still pending in the buffer to the file, closes the file, and releases any memory used for the file. The EOF is a constant defined in the header file stdio.h. There are various functions provided by C standard library to read and write a file, character by character, or in the form of a fixed length string.

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Intro to File Input/Output in C, All that means is that to read in data, we use scanf() (or a few other functions) and to In fact, C has a general mechanism for reading and writing files, which is or some other problem occurred (e.g., it sees a letter when it is trying to read in a​  This is an optional starting asterisk indicates that the data is to be read from the stream but ignored, i.e. it is not stored in the corresponding argument. 2: width. This specifies the maximum number of characters to be read in the current reading operation. 3: modifiers

File I/O : Learn to open, close, write and read form files in C, Let's see how to write data in a file, open, close or read a file. Opening a file. We open a file or create a new file using fopen() function. Let's look at the syntax of  I am trying to read a .dat file to decrypt it. It is homework so I dont want the answer. I am just trying to figure out what it is that I am doing wrong to find the answer. This is what I have so far. I cant figure out what else I am missing.

Comments
  • Can you store the absolute path of the .dat file in string f.
  • 1) .cpp is not executed, it's compiled 2) executable file is not executed from folder Assignment3.1 and that's why you can't read from data file
  • but the check returns False then you are not reading your file
  • @GrzegorzAdamKowalski thank you for the slightly valuable input.
  • @KillzoneKid thank you for the slightly valuable input.
  • This does solve the fact that I was getting different outputs each time I ran the program but does not solve the inability to read the .dat file
  • Does file exist in same folder where program is being run?