Question

I am trying to write data to a binary file and then read back the data from the file. The data consists of a single number (an integer) nrows. Below is my code for writing the data to a binary file. However, when I try to read back the data and print the result using printf, I obtain a nonsensical result: -2.

FILE *fout;
FILE *file_pointer;
int nrows = 5;

fout = fopen("matrixB.bin", "wb") //Writing to a binary file.//

fwrite(&nrows, sizeof(int), 1, fout); //Writing the number nrows to the binary file "matrixB.bin"//

file_pointer = fopen("matrixB.bin", "rb"); //Reading a binary file.//

fread(&nrows, sizeof(int), 1, file_pointer);

printf("%d", nrows); //Here -2 is printed, instead of 5.//

What is the problem with my code?

Answer 1

One of the characteristics of the C file functions (fread, fwrite, etc) is that they normally perform buffered I/O.

Your program doesn’t flush and/or close the file before reopening it. It should.