C, Document Reading and Writing

If  processed binary file, use the following access mode to replace the above:

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

closed file

To close the file, please use the fclose() function. The prototype of the function is as follows:

int  fclose ( FILE *fp );

• If the file is closed successfully, the fclose() function returns zero, and if the error returns EOF. This function, in fact, removes the data from the buffer, closes the file, and releases all the memory used for that file. EOF is a constant defined in the header file  stdio.h 

The C standard library provides various functions to read and write files by characters or as a fixed-length string.

Write to the file

Here are the simplest functions to write characters to the stream:

int  fputc ( int  c , FILE *fp );

The function fputc () writes the character value of the parameter c into the output stream that the fp points to. If the writes are successful, it returns the written character and the EOF if an error occurs. You can use the following function to write a string ending with a null to the stream:

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

 The function fputs () writes the string s to the output stream where the fp points to. If the writes succeed, it returns a non-negative value and the EOF if an error occurs. You can also use the function of int fprintf (FILE * fp, const char * format,...)  writes a string to the file. Try the following example:

 Note:Make sure that you have an available tmp directory, and if it does not exist, you need to create it on your computer first.

/ tmp is usually a temporary directory on the Linux system. If you run on the Windows system, you need to modify it to an existed directory in the local environment, such as: C: \ tmp, D: \ tmp, etc.

living example

#include <stdio.h > int  main () { FILE  *fp  = NULL ; 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 creates a new file test.txt inthe / tmp directory. And  writes to two lines using two different functions. Let's read this file next.

Read the file

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

int  fgetc ( FILE * fp );

The fgetc () function reads a character from the input file to which the fp points. The return value is the read character and the EOF if an error occurs. The following function allows you to read a string from a stream:

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

 The function fgets () reads n-1 characters from the input stream directed by fp. It copies the read string to the buffer buf and appends a null character at the end to terminate the string.

If this function encounters a broken line character '\ n' or the  EOF of the end of file before reading the last character, then only returned to the read characters, including line breaks. You can also use the int fscanf (FILE * fp, const char * format,...) function to read the string from the file, but it stops reading when encountering the first space and line break.

living example

#include <stdio.h > int  main () { FILE  *fp  = NULL ; 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 reads the files created in the previous section, producing the following results:

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

3: This  is  testing for  fputs...

First, the method of fscanf()  only reads This .because it encounters a space in the back. Second, call functon fgets () to read the remaining part until the end of the line. Finally, call fgets () to read the second row completely.

Binary I / O function

The following two functions are used for the binary input and output:

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 );

 Both functions are read and write for storage blocks-usually arrays or structures.

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