Your SlideShare is downloading. ×
  • Like
7.0 files and c input
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×

Now you can save presentations on your phone or tablet

Available for both IPhone and Android

Text the download link to your phone

Standard text messaging rates apply

7.0 files and c input

  • 179 views
Published

 

Published in Technology
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
    Be the first to like this
No Downloads

Views

Total Views
179
On SlideShare
0
From Embeds
0
Number of Embeds
0

Actions

Shares
Downloads
6
Comments
0
Likes
0

Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
    No notes for slide

Transcript

  • 1. Files and C Input/Output
  • 2. Learning outcomes  At the end of this section you will be able to  Understand the concepts involved in accessing secondary storage by computer programs  Understand how to deal with disk files in C  Write programs those read and write into files in a secondary storage
  • 3. Introduction  All input and output in C are from and to files.  File is a sequence of bytes. (text files use n)  Open, Process, Close  An open file is identified by a “File Access Control Block”
  • 4. File Access Control Blocks  struct iobuf { char *_ptr; // Current ch. position int *_cnt; // Remaining bytes char *_base; // Buffer base address char _flag; // Access control flags char _file; } // File number  #define FILE struct _iobuf /* stdio.h */  #define EOF -1  typedef struct _iobuf FILE;
  • 5. FCB’s cont…  First 3 file access control blocks are automatically assigned to  standard input  standard output and  standard error devices  FILE *stdin, *stdout, *stderr  Standard input and output devices can be redefined for a program at the command line as,  Process <infile >outfile
  • 6. stdio.h  Many IO libray functions come in pairs (or in triplets) whose operational differs only slightly.  printf(“Hello world”); // prints to stdout  fprintf(fp,“Hello world”) // prints to a file identified by fp  fprintf(stdout,“Hello world”) // same as the first  fp is a pointer to a file access control block and is returned by a successful fopen() operation.
  • 7. fopen() FILE *fp; /* declares a file pointer or a stream */ char s[]=“c:mydirtemp.txt”; If ((fp=fopen(s,“wt”)) == NULL) printf(“file open error”);  Mode string  “r | w | a [+] [ t | b ]”  r : open for read  w : create for write  a : open for append/create for write  + : permits both read and write  t | b : in text or binary mode
  • 8. fclose()  To close an opened file,  if (fclose(fp)!=0) printf(“file close error”);  If necessary file’s buffer is first flushed (written back to the file) before it is closed.  fclose() is automatically called for each open file when a program terminates normally.
  • 9. Character transfers to/from files  getc(fp) and fgetc((fp) reads a ch from the stream fp.  putc(c,fp) and fputc(c,fp) writes c into the stream fp.  ungetc(c,fp) push back the character just read to fp.  All 5 returns the ch. on success and EOF on failure Eg – while ((*ptr++=getc(fp))!=EOF) …; while (putc(*ptr++)) …;  #define getchar() getc(stdin)  #define putchar(c) putc(c,stdout) // in stdio.h
  • 10. Line IO  Line  ch sequence terminating in a ‘n’  Simplest form of a record in a C file.  fgets(s,n,fp) reads the next line (including ‘n’) up to a maximum of n chs from stream fp and writes into memory buffer starting from s with a terminating ‘0’.  gets(s) reads a line from stdin and placed in memory starting from s, ‘n’ replaced by a ’0’.  gets() and fgets() return s on success and a NULL on failure.
  • 11.  fputs(s,fp) writes a string beginning at s onto the stream fp without ‘0’.  puts(s) same as fputs(s,stdout) but appends a ‘n’.  puts() fputs() returns last ch or 0 on success and EOF on failure.  These return values permit statements such as,  while(strlen(gets(s)) …;  while (fgets(s,MAX_LINE,fp1) != NULL) fputs(s,fp2);
  • 12. Formatted IO  The characters –123.45E-7 printed on a display or typed in a keyboard is totally different from the form it is stored in memory.  printf(f), fprintf(fp,f), sprintf(s,f) - Return the no. of bytes output on success and EOF on failure.  Eg- printf(“nAverage = %-8.4f”,avg);  scanf(f), fscanf(fp,f), sscanf(s,f) – On success return the no. of fields scanned and stored. Return EOF on failure.
  • 13. Binary IO  fread(ptr,i,n,fp)  Transfers n data blocks of each of size i bytes from stream fp into memory buffer at ptr.  Returns the no.of blocks read.  fwrite(ptr,i,n,fp)  Appends n data items in memory at ptr each of size i to the stream fp.  Returns no. of bytes written.
  • 14. Further File Operations  unlink(“fname”)  removes fname from the file system  rewind(fp)  set the current file position at start of file.  fseek(fp,L,i)  place the file position L bytes from i  i is 0|1|2 for start | current | end  L is a long integer  unlink and fseek return 0 on success and –1 on failure. rewind does not return any value.  ftell(fp)  returns current byte position as a long and -1 on failure  feof() detects end-of-file marker in a file