File I/O in C

[plenderj]

Howdy.
Just wondering if anyone could give me some sample source for File I/O in C ?

Cheers,
Jamie.

[kedaman]

Here's some ANSI-C documentation for you
http://www.hh.se/stud/d98rolb/ansi/main.html

[plenderj]

Oh cool thanks!

[jim mcnamara]

basic i/o functions
fopen("filename","mode") where mode = w,r,r+,wb,rb,rb+....
Here are a bunch of code snippets

listing 9-2
FILE *fp; 

fp = fopen("test", "w"); 

listing 9-3
FILE *fp; 

if ((fp = fopen("test","w"))==NULL) {
  printf("Cannot open file.\n");
  exit(1);
} 

listing 9-4
do {
  ch = getc(fp);
} while(ch!=EOF); 

listing 9-5
/* KTOD: A key to disk program. */ 
#include <stdio.h>
#include <stdlib.h> 

void main(int argc, char *argv[])
{
  FILE *fp;
  char ch; 

  if(argc!=2) {
    printf("You forgot to enter the filename.\n");
    exit(1);
  } 

  if((fp=fopen(argv[1], "w"))==NULL) {
    printf("Cannot open file.\n");
    exit(1);
  } 

  do {
    ch = getchar();
    putc(ch, fp);
  } while (ch!='
listing 9-6
/* DTOS: A program that reads files and displays them
         on the screen. */ 
#include <stdio.h>
#include <stdlib.h>
 
void main(int argc, char *argv[])
{
  FILE *fp;
  char ch; 

  if(argc!=2) {
    printf("You forgot to enter the filename.\n");
    exit(1);
  } 

  if((fp=fopen(argv[1], "r"))==NULL) {
    printf("Cannot open file.\n");
    exit(1);
  } 

  ch = getc(fp);   /* read one character */

  while (ch!=EOF) {
    putchar(ch);  /* print on screen */
    ch = getc(fp);
  } 
  fclose(fp);
} 

listing 9-7
while(!feof(fp)) ch = getc(fp); 

listing 9-8
/* Copy a file. */ 
#include <stdio.h>
#include <stdlib.h> 

void main(int argc, char *argv[])
{
  FILE *in, *out;
  char ch; 

  if(argc!=3) {
    printf("You forgot to enter a filename.\n");
    exit(1);
  } 

  if((in=fopen(argv[1], "rb"))==NULL) {
    printf("Cannot open source file.\n");
    exit(1);
  }
  if((out=fopen(argv[2], "wb")) == NULL) {
    printf("Cannot open destination file.\n");
    exit(1);
  } 

  /* This code acutally copies the file. */
  while(!feof(in)) {
    ch = getc(in);
    if(!feof(in)) putc(ch, out);
  } 

  fclose(in);
  fclose(out);
} 

listing 9-9
#include <stdio.h>
#include <stdlib.h>
#include <string.h> 

void main(void)
{
  char str[80];
  FILE *fp; 

  if((fp = fopen("TEST", "w"))==NULL) {
    printf("Cannot open file.\n");
    exit(1);
  }

  do {
    printf("Enter a string (CR to quit):\n");
    gets(str);
    strcat(str, "\n");  /* add a newline */
    fputs(str, fp);
  } while(*str!='\n');
} 

listing 9-10
#include <stdio.h>
#include <stdlib.h>
#include <string.h> 

void main(void)
{
  char str[80];
  FILE *fp; 

  if((fp = fopen("TEST", "w+"))==NULL) {
    printf("Cannot open file.\n");
    exit(1);
  }

  do {
    printf("Enter a string (CR to quit):\n");
    gets(str);
    strcat(str, "\n");  /* add a newline */
    fputs(str, fp);
  } while(*str!='\n');

  /* now, read and display the file */
  rewind(fp);  /* reset file position indicator to
                  start of the file. */
  while(!feof(fp)) {
    fgets(str, 79, fp);
    printf(str);
  }
} 

listing 9-11
/* The program substitutes spaces for tabs
   in a text file and supplies error checking. */

#include <stdio.h>
#include <stdlib.h> 

#define TAB_SIZE 8 
#define IN 0 
#define OUT 1 

void err(int e); 

void main(int argc, char *argv[])
{
  FILE *in, *out;
  int tab, i;
  char ch;

  if(argc!=3) {
    printf("usage: detab <in> <out>\n");
    exit(1);
  } 

  if((in = fopen(argv[1], "rb"))==NULL) {
    printf("Cannot open %s.\n", argv[1]);
    exit(1);
  } 

  if((out = fopen(argv[2], "wb"))==NULL) {
    printf("Cannot open %s.\n", argv[1]);
    exit(1);
  } 

  tab = 0;
  do {
    ch = getc(in);
    if(ferror(in)) err(IN); 

    /* if tab found, output appropriate number of spaces */
    if(ch=='\t') {
      for(i=tab; i<8; i++) {
        putc(' ', out);
        if(ferror(out)) err(OUT);
      }
      tab = 0;
    }
    else {
      putc(ch, out);
      if(ferror(out)) err(OUT);
      tab++;
      if(tab==TAB_SIZE) tab = 0;
      if(ch=='\n' || ch=='\r') tab = 0;
    }
  } while(!feof(in));
  fclose(in);
  fclose(out);
} 

void err(int e)
{
  if(e==IN) printf("Error on input.\n");
  else printf("Error on output.\n");
  exit(1);
} 

listing 9-12
/* Double check before erasing. */ 
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h> 

main(int argc, char *argv[])
{
  char str[80];

  if(argc!=2) {
    printf("usage: xerase <filename>\n");
    exit(1);
  } 

  printf("Erase %s? (Y/N): ", argv[1]);
  gets(str);
 
  if(toupper(*str)=='Y')
    if(remove(argv[1])) {
      printf("Cannot erase file.\n");
      exit(1);
    } 
  return 0;  /* return success to OS */
} 

listing 9-13
/* Write some non-character data to a disk file
   and read it back.  */
#include <stdio.h>
#include <stdlib.h>

void main(void)
{
  FILE *fp;
  double d = 12.23;
  int i = 101;
  long l = 123023L; 

  if((fp=fopen("test", "wb+"))==NULL) {
    printf("Cannot open file.\n");
    exit(1);
  } 

  fwrite(&d, sizeof(double), 1, fp);
  fwrite(&i, sizeof(int), 1, fp);
  fwrite(&l, sizeof(long), 1, fp); 

  rewind(fp); 

  fread(&d, sizeof(double), 1, fp);
  fread(&i, sizeof(int), 1, fp);
  fread(&l, sizeof(long), 1, fp); 
  printf("%f %d %ld", d, i, l);

  fclose(fp);
} 

listing 9-14
struct struct_type {
  float balance;
  char name[80];
} cust; 


listing 9-19
#include <stdio.h>
#include <stdlib.h> 

void main(int argc, char *argv[])
{ 
  FILE *fp;

  if(argc!=3) {
    printf("Usage: SEEK filename byte\n");
    exit(1);
  } 

  if((fp = fopen(argv[1], "r"))==NULL) {
    printf("Cannot open file.\n");
    exit(1); 
  } 

  if(fseek(fp, atol(argv[2]), SEEK_SET)) {
    printf("Seek error.\n");
    exit(1);
  }

  printf("Byte at %ld is %c.\n", atol(argv[2]), getc(fp));
  fclose(fp);
} 

listing 9-20
fseek(fp, 9*sizeof(struct list_type), SEEK_SET); 

listing 9-21
/* fscanf() - fprintf() example */ 
#include <stdio.h> 
#include <io.h>
#include <stdlib.h> 

void main(void)
{
  FILE *fp;
  char s[80];
  int t; 

  if((fp=fopen("test", "w")) == NULL) {
    printf("Cannot open file.\n");
    exit(1);
  } 

  printf("Enter a string and a number: ");
  fscanf(stdin, "%s%d", s, &t); /* read from
                                   keyboard */

  fprintf(fp, "%s %d", s, t); /* write to file */
  fclose(fp); 

  if((fp=fopen("test","r")) == NULL) {
    printf("Cannot open file.\n");
    exit(1);
  } 

  fscanf(fp, "%s%d", s, &t); /* read from file */
  fprintf(stdout, "%s %d", s, t); /* print on
                                     screen */
} 

listing 9-24
#include <stdio.h> 

void main(void)
{
  char str[80]; 

  printf("Enter a string: ");
  gets(str);
  printf(str);
} 

listing 9-25
TEST > OUTPUT 

listing 9-26
TEST < INPUT > OUTPUT 

listing 9-27
#include <stdio.h> 

void main(void)
{
  char str[80]; 

  freopen("OUTPUT", "w", stdout);
  printf("Enter a string: ");
  gets(str);
  printf(str);
} 

listing 9-28
int fd; 
if((fd=open(filename, mode)) == -1) {
  printf("Cannot open file.\n");
  exit(1);
} 

listing 9-30
/* Read and write using unbuffered I/O */ 
#include <stdio.h>
#include <io.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h> 

#define BUF_SIZE  128 

void input(char *buf, int fd1);
void display(char *buf, int fd2); 

void main(void)
{
  char buf[BUF_SIZE];
  int fd1, fd2; 

  if((fd1=open("test", O_WRONLY))==-1){ /* open for write */
    printf("Cannot open file.\n");
    exit(1);
  } 

  input(buf, fd1); 

  /* now close file and read back */
  close(fd1); 
  if((fd2=open("test", O_RDONLY))==-1){ /* open for read */
    printf("Cannot open file.\n");
    exit(1);
  } 

  display(buf, fd2);
  close(fd2);
} 

/* Input text. */
void input(char *buf, int fd1)
{
  register int t;
  do {
    for(t=0; t<BUF_SIZE; t++) buf[t] = '\0';
    gets(buf); /* input chars from keyboard */
    if(write(fd1, buf, BUF_SIZE)!=BUF_SIZE) {
      printf("Error on write.\n");
      exit(1);
    }
  } while (strcmp(buf, "quit"));
} 

/* Display file. */
void display(char *buf, int fd2)
{
  for(;;) {
    if(read(fd2, buf, BUF_SIZE)==0) return;
    printf("%s\n", buf);
  }
} 

listing 9-31
/* Demonstrate lseek(). */ 
#include <stdio.h>
#include <io.h>
#include <stdlib.h>
#include <fcntl.h>

#define BUF_SIZE  128 

void main(int argc, char *argv[])
{
  char buf[BUF_SIZE+1], s[10];
  int fd, sector;

  if(argc!=2) {
    printf("usage: dump <sector>\n");
    exit(1);
  } 

  buf[BUF_SIZE] = '\0'; /* null terminate buffer */

  if((fd=open(argv[1], O_RDONLY))==-1) {
    printf("Cannot open file.\n");
    exit(1);
  } 

  do {
    printf("\nBuffer: ");
    gets(s); 

    sector = atoi(s); /* get the sector to read */

    if(lseek(fd, (long)sector*BUF_SIZE, 0)==-1L)
      printf("Seek Error\n"); 
    if(read(fd, buf, BUF_SIZE)==0) {
      printf("Sector Out Of Range\n");
    }
    else
      printf(buf);
  } while(sector>=0);
  close(fd);
}

[plenderj]

Cheers for that too

[jim mcnamara]

Frank Herbert strikes again... see that you read Dune, so did I, about 45 years ago.

[plenderj]

Yeah on the 3rd book of the dune series at the mo, and lovin' it !

[kedaman]

Cool, Jamie, can i have the titles for the three first ones (I might get some time to read them

[plenderj]

Dune
Dune Messiah
Children of Dune
God Emperor of Dune
Heretics of Dune
Chapterhouse: Dune

I can lend you any of the first three if you don't have them... don't have the rest myself though.

[kedaman]

That would be cool, but how do you mean lend them?

[plenderj]

Well you give me your address, I stick them in the post to you, you read them, and then send them back

[kedaman]

Alrite That sounds pretty simple
see you @ icq?

[Zaei]

I've read the first 4... then got bored =). So I went and read the wheel of time series again. Now it's Lord of the rings for the first time (stupid programming... I havent had to renew a book from the library in like, ten years!)

Z.