If the file does not exist, fopen returns NULL. If the file exists, its contents are overwritten. If the file does not exist, it will be created.
In this C programming tutorial we are going to talk about the use of binary files. Binary files Binary files are very similar to arrays of structures, except the structures are in a disk-file rather than an array in memory. Binary files have two features that distinguish them from text files: You can instantly use any structure in the file.
You can change the contents of a structure anywhere in the file.
After you have opened the binary file, you can read and write a structure or seek a specific position in the file. A file position indicator points to record 0 when the file is opened. A read operation reads the structure where the file position indicator is pointing to.
After reading the structure the pointer is moved to point at the next structure. A write operation will write to the currently pointed-to structure. After the write operation the file position indicator is moved to point at the next structure. The fseek function will move the file position indicator to the record that is requested.
This chapter explains the features, technical details and syntaxes of the C programming language. I assume that you could write some simple programs. Extend your 50g with C - Part 1. Introduction. This lengthy article explains why you would and how you can extend the functionality of your 50g using C. Complete examples are provided to illustrate how to create high performance mathematical routines such as a complex LogGamma function, a sparse linear solver, and a 2D convex hull.. There are two reoccurring themes in this article. Here is a function to launch a background process in PHP. Finally created one that actually works on Windows too, after a lot of reading and testing different approaches and parameters.
Remember that you keep track of things, because the file position indicator can not only point at the beginning of a structure, but can also point to any byte in the file.
The fread and fwrite function takes four parameters: A memory address Number of bytes to read per block Number of blocks to read A file variable For example: Only one block is requested. Changing the one into ten will read in ten blocks of x bytes at once. In the main function we open fopen a file for writing w.
Then we check if the file is open, if not, an error message is displayed and we exit the program. Then we write the record to the file. We do this ten times, thus creating ten records.
Take a look at the example: With the fread we read-in the records one by one. After we have read the record we print the member x of that record.
The only thing we need to explain is the fseek option. The function fseek must be declared like this: The new position, measured in characters from the beginning of the file, is obtained by adding offset to the position specified by whence. Three macros are declared in stdio. Using negative numbers it is possible to move from the end of the file.
This counter is then used in the fseek statement to set the file pointer at the desired record. The result is that we read-in the records in the reverse order. The function rewind can be used like this: Then we rewind to first position in the file.
Then read-in all records and print the value of member x. Without the rewind you will get garbage. That is all for this tutorial.
This entry was posted in C Tutorials.
You can follow any responses to this entry through the RSS 2. Both comments and pings are currently closed.Jan 03, · appending data to binary file fstream. C / C++ Forums on Bytes. size_t fwrite (const void * ptr, size_t size, size_t count, FILE * stream); Write block of data to stream Writes an array of count elements, each one with a size of size bytes, from the block of memory pointed by ptr to the current position in the stream.
C Tutorial – Binary File I/O In an earlier tutorial we talked about file I/O functions and the use of text files. In this C programming tutorial we are going to talk about the use of binary files.
|Simplest programming tutorials for beginners||Once a stream is in binary mode, it cannot be reset to nonbinary mode. The stream must be opened for reading or an IOError will be raised.|
|Simplest programming tutorials for beginners||Crashes If you have not already reset your 50g, take your paper clip and reset your 50g using the reset hole on the back of the 50g. Expect to do this frequently.|
Extend your 50g with C - Part 1. Introduction. This lengthy article explains why you would and how you can extend the functionality of your 50g using C. Complete examples are provided to illustrate how to create high performance mathematical routines such as a complex LogGamma function, a sparse linear solver, and a 2D convex hull..
There are two reoccurring themes in this article. I have to write numerical data to binary files. Since some of the data vectors I deal with can be several gigs in size, I have learned not to use C++ iostreams. Instead I want to use C File*. In this tutorial, you'll learn how to do file IO, text and binary, in C, using fopen, fwrite, and fread, fprintf, fscanf, fgetc and fputc..
FILE * For C File I/O you need to use a FILE pointer, which will let the program keep track of the file being accessed.