Linux Learning 7-file operations

Standard I/O library common functions use

1.fopen functions: Input and output for files and terminals.

#include <stdio.h>

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

2.fclose function: Closes the specified file stream stream.

#include <stdio.h>

int fclose (FILE *stream);

3.GETCWD function: Writes the name of the current directory to BUF.

#include <unistd.h>

char* getcwd (char* buf, size_t size);

#include <stdio.h>#include<unistd.h>int  main () {    char Acfilepath [[] = {0};     sizeof (Acfilepath));    printf ("path is%s \ r \ n",    acfilepath); return 0 ;}

Ex

4.fgets function: Reads a string from the input file stream stream.

#include <stdio.h>

Char *fgets (char *s, int n, FILE *stream);

Fgets writes a string into the string that s points to, until one of the following occurs:

• Encountering line breaks
• N-1 characters have been transferred
• Reach the end of the file.

It also passes the newline symbol encountered to the receiving string , plus a null byte to the end. You can transfer up to n-1 characters at a time.

5 format input and output

#include <stdio.h>

int fprintf (FILE *stream, const char *format, ...)

Sends its own output to a specified file stream.

#include <stdio.h>int  main () {    *pfile = fopen ("/home/xiaodeyao/wzh/code/3_ Io/new.txt","wb+");     " The NUM is%d and the string is%s " 1024x768 " Hello world! " );     return 0 ;}

Ex

#include <stdio.h>

int fscanf (FILE *stream, const char *format, ...)

Reads formatted input from stream stream.

#include <stdio.h>intMain () {FILE*pfile = fopen ("/home/xiaodeyao/wzh/code/3_io/fscanf.txt","R"); intA =0; Characdate[ -] = {0}; floatDou =0; Charc =0; FSCANF (Pfile,"%d%s%c%f", &a, Acdate, &c, &Dou); printf ("%d,%s,%c,%f\r\n", A, acdate, C, Dou); return 0;}

Ex

PS: Here is the file mod if "W", there will be a problem. But in some cases, "w" can be used. Example: http://www.runoob.com/cprogramming/c-function-fscanf.html

Here's a little bit of a dig.

6.fseek ()

Specifies the location for the next file read and write operation.

int fseek (FILE *stream, long int offset, int whence)

Stream-This is a pointer to the file object that identifies the stream.
Offset-This is the relative whence, in bytes.
Whence-This is where you start adding offset offsets. It is generally specified as one of the following constants:
Constant description
The beginning of the Seek_set file
Seek_cur the current position of the file pointer
Seek_end the end of the file

#include <stdio.h>intMain () {FILE*FP; FP= fopen ("file.txt","w+"); Fputs ("This is w3cschool.cc", FP); Fseek (FP,7, Seek_set); Fputs ("C Programming Langauge", FP);      Fclose (FP); return(0);}

Ex

7.ftell ()

Long int ftell (FILE *stream)

Parameters
Stream-This is a pointer to the file object that identifies the stream.
return value
The function returns the current value of the position identifier. If an error occurs, -1l is returned, and the global variable errno is set to a positive value.

#include <stdio.h>intMain () {FILE*FP; intLen; FP= fopen ("file.txt","R"); if(fp = =NULL) {Perror ("Open File Error"); return(-1); } fseek (FP,0, Seek_end); Len=Ftell (FP);   Fclose (FP); printf ("Total size of file.txt =%d bytes \ n", Len); return(0);}

Ex

Reference:

Http://www.runoob.com/cprogramming/c-function-ftell.html

Linux Learning 7-file operations