C document literacy

open a file

You can use thefopen () function to create a new document or open an existing file, the call will initialize an object of type FILE,FILE type contains all the information necessary to control the flow. Here is the prototype of this call:

FILE *fopen( const char * filename, const char * mode );

Here, filename is a string used to name the file access mode modevalue can be one of the following values:

If the process is a binary file, you need to use the following access mode access mode to replace the above:

"rb", "wb", "ab", "rb+", "r+b", "wb+", "w+b", "ab+", "a+b"

Close the file

To close a file, use fclose () function. Function prototype is as follows:

 int fclose( FILE *fp );

If successful, close thefile, fclose () function returns zero, an error occurs when closing the file, the function returns EOF.This function is in fact, will clear the data in the buffer, close the file, and releases all memory for the file. EOF is a constant defined in the header filestdio.h in.

C standard library provides a variety of functions to press a character or in the form of fixed-length string to read and write files.

Write to file

Here is the write characters to a stream of the most simple function:

int fputc( int c, FILE *fp );

Functionfputc () writes the character c to the value of the parameter fp points to the output stream.If the write is successful, it returns the character written, if an error occurs, it returnsEOF.You can use the following functions to a null-terminated string to be written to the stream:

int fputs( const char *s, FILE *fp );

Functionfputs () writes the string sto fp points to the output stream. If the write is successful, it will return a non-negative value if an error occurs, it returnsEOF.You can also useint fprintf (FILE * fp, const char * format, ...) function to write a string to be written to a file.Try the following examples:

Note: Make sure you have available the / tmpdirectory, if this directory does not exist, you'll need to create the directory on your computer.

#include <stdio.h>

main()
{
   FILE *fp;

   fp = fopen("/tmp/test.txt", "w+");
   fprintf(fp, "This is testing for fprintf...\n");
   fputs("This is testing for fputs...\n", fp);
   fclose(fp);
}

When the above code is compiled and executed, it will be created in the / tmp directory, a new filetest.txt, and use two different functions written two lines.Let us read the file.

Read the file

Here is the simplest function to read a single character from a file:

int fgetc( FILE * fp );

fgetc () function reads a character from the input file pointed to by fp.The return value is a character read, if an error occurs returnsEOF.The following function allows you to read a string from the stream:

char *fgets( char *buf, int n, FILE *fp );

Functionfgets () reads n from the input stream pointed to by fp - the one character.It will read the string copied into the bufferbuf, and finally appends a nullcharacter to terminate the string.

If the function before reading the last character encountered a newline character '\ n' at the end of the file or EOF, only to return to read the characters, including newline. You can also useint fscanf (FILE * fp, const char * format, ...) function to read a string from a file, but in the face of the first space character, it will stop reading.

#include <stdio.h>

main()
{
   FILE *fp;
   char buff[255];

   fp = fopen("/tmp/test.txt", "r");
   fscanf(fp, "%s", buff);
   printf("1 : %s\n", buff );

   fgets(buff, 255, (FILE*)fp);
   printf("2: %s\n", buff );
   
   fgets(buff, 255, (FILE*)fp);
   printf("3: %s\n", buff );
   fclose(fp);

}

When the above code is compiled and executed, it will read files created on a part, produces the following results:

1 : This
2: is testing for fprintf...

3: This is testing for fputs...

First, fscanf () method only read This,because it encounters a space in the back. Next, call thefgets () to read the rest, until the end of the line.Finally, callfgets () read in its entirety the second line.

Binary I / O functions

The following two functions for binary inputs and outputs:

size_t fread(void *ptr, size_t size_of_elements, 
             size_t number_of_elements, FILE *a_file);
              
size_t fwrite(const void *ptr, size_t size_of_elements, 
             size_t number_of_elements, FILE *a_file);

These two functions are used to read and write memory block - usually an array or a structure.