If the file does not exist, fopen returns NULL.
Prev NEXT Binary files are very similar to arrays of structures, except the structures are in a disk file rather than in an array in memory. Because the structures in a binary file are on disk, you can create very large collections of them limited only by your available disk space.
They are also permanent and always available. The only disadvantage is the slowness that comes from disk access time. Binary files have two features that distinguish them from text files: You can jump instantly to any structure in the file, which provides random access as in an array.
You can change the contents of a structure anywhere in the file at any time. Binary files also usually have faster read and write times than text files, because a binary image of the record is stored directly from memory to disk or vice versa.
In a text file, everything has to be converted back and forth to text, and this takes time. C supports the file-of-structures concept very cleanly.
Once you open the file you can read a structure, write a structure, or seek to any structure in the file.
This file concept supports the concept of a file pointer. When the file is opened, the pointer points to record 0 the first record in the file. Any read operation reads the currently pointed-to structure and moves the pointer down one structure. Any write operation writes to the currently pointed-to structure and moves the pointer down one structure.
Seek moves the pointer to the requested record. Keep in mind that C thinks of everything in the disk file as blocks of bytes read from disk into memory or read from memory onto disk.
C uses a file pointer, but it can point to any byte location in the file. You therefore have to keep track of things. The following program illustrates these concepts: You can see that fopen and fclose work exactly as they did for text files.
The new functions here are fread, fwrite and fseek. The fread function takes four parameters: One block of 12 bytes is requested. It would be just as easy to read blocks from disk into an array in memory by changing 1 to The fwrite function works the same way, but moves the block of bytes from memory to the file.
The fseek function moves the file pointer to a byte in the file.
Generally, you move the pointer in sizeof struct rec increments to keep the pointer at record boundaries. You can use three options when seeking: Several different options appear in the code above.
This opens the file for reading and writing, which allows records to be changed. The code seeks to a record, reads it, and changes a field; it then seeks back because the read displaced the pointer, and writes the change back. For more information on C and related topics, check out the links below.C Input Output (I/O) This tutorial focuses on two in-built functions printf() and scanf() to perform I/O task in C programming.
Also, you will learn to write a valid program in C. just google "c file manipulation" an read, if you know any C at all you should be able to understand this, otherwise just ask you Prof.
for help – cmaynard Nov 7 '09 at @GMan: Since this is a built-in feature of most logging libraries, there aren't many reasons to re-invent it. Input/output with files; Set the initial position at the end of the file. If this flag is not set, the initial position is the beginning of the file.
For example, in the case that we try to write to a file that is not open for writing or if the device where we try to write has no space left. Write a C program that displays contents of a given file like 'more' utility in Linux Set position with seekg() in C++ language file handling Program to delete a line given the line number from a file.
tive, you can always write your program in C/C++ and then compile it on different operating systems and tweak each version to make it run under specific operating systems.
06 Chqxd 11/4/03 PM Page Your programming skill and experience also determine the programming lan-. How to Create a First C Program on Linux. Yet another typical source of problems is forgetting the.c extension at the end of the name of the source code file(s).
Running hello. The result will be to write the text Hello, world! on the monitor screen.