File opening modes and file pointer c tutorial

This C programming tutorial explains following concepts

1. Open a c file and what are the opening modes
2. What is a File pointer
3. Close a c file
4. Read and write character to a file

How to open a file using c language? Also discuss its different file opening modes.

File Opening:

• Before read or write operation, a file should be opened.
• All standard file handing function of C are declared in stdio. h header file
• When a file is opened a point of memory is reserved for file to read and write this memory is called memory buffer.
• When a file is read it is first stored in the memory buffer and then program reads the file from the memory buffer.
• When a file is written, then it is written in buffer, then its contents are transferred on the disk.
• The transfer of data from buffer to the disk is called flushing of buffer.
• The writing and reading through file through disk is time consuming, therefore time of reading and writing data to a file is reduced through buffer.

 See code example: write data into a text file c++ program

The File Pointer:

• A pointer is like a variable whose content is the address of another memory cell (variable).
• Represents a pointer to the variable with which it is used.
• A file is not directly accessible in C.
• File are accessed through I\O buffers.
• A file pointer is a variable of FILE type defined in stdio.h
• FILE* represents a pointer to a variable of FILE type.
• The fopen( )function is used to open a file.

 Prototype is: FILE*fopen(const char*filename,const char*mode);
 OR
 FILE*fp; // it specifies the file pointer.
 Fp=fopen(file,mode);

File opening Modes:

• “r” open text file for reading,each file must exists before reading.
• “w” open a text file for writing, if the file already exists then its contents are overwritten, if it does not exists, it will be created.
• “a” open a text file for append. Data is appended at the end of existing file. If the file does not exist, it will be created.
• “r+” open a file for both reading and writing. The file must already exists
• “w+” open a file for reading and writing, its contents are overwritten if the file does not exist, it is created.
• “a+” open a text file for both reading and appending. If the file does not exist, it is created for both reading and writing.

see example code: Append data into a text file c programming source code

The fopen function returns the null pointer, if it fails to open the file (most common reason is file does not exist).

How to close a file in the c language?
File Closing:

• An open must be close after completing the task.
• When a file is close then the buffer is flushed (data is transferred on the disk).
• If the file is not close than the data may be lost.
• The fclose () function is used to close a file.
• Syntax:

fclose(fp);
Where fp is a file pointer associated to a file which is to be closed.
fclose () function returns 0 if the close operation is successfully completed.
fclose () function returns EOF if any error occurs.

How to read and write character to a file using C language?

• Once a file has been opened depending on its opening mode then either a character can be read from a file or character can be written to a file using the following function
• Putc( ):
• The putc( ) function writes a single character to the file.
• The putc ( ) function returns the characters, if it successfully writes it.
• The putc ( ) function returns the EOF if an error occurs.

Syntax:
putc(character ch , file_pointer);

see example: copy data from one text file to another c source code

Character ch can be character, int, constant or a variable.
File pointer specifies variable of FILE type associated with the file in witch character is to be written.