<< Chapter < Page Chapter >> Page >

Output:

File opened successfully. Contents: String: 111 222 3String: 33String: 444 555 6String: 66 String: 777 888 9String: 99Now closing file...

The main area of focus is the while loop - notice how I performed the check for the return of a NULL pointer. Remember that passing in char * variable, c as the first argument assigns the line read into c, which is printed off by printf. We specified a maximum number of characters to be 10 - we knew the number of characters per line in our text file is more than this, but we wanted to show that fgets reads 10 characters at a time in this case.

Notice how fgets returns when the newline character is reached - this would explain why 444 and 777 follow the word "String". Also, the tab character, \t, is treated as one character.

Other function:

Fseek() function

int fseek (FILE *fp, long int offset, int origin);

In the above prototype, there are two arguments:

  • fp: Pointer to a FILE object that identifies the stream.
  • offset: Number of bytes to offset from origin.
  • If offset>= 0: set the position indicator toward to the end of file,
  • If offset<0: set the position indicator toward to the beginning of file.
  • origin: Position from where offset is added. It is specified by one of the following constants defined in<cstdio>:
Constant Value Meaning
SEEK_SET 0 Beginning of file
SEEK_CUR 1 Current position of the file pointer
SEEK_END 2 End of file

This function sets the position indicator associated with the fp to a new position defined by adding offset to a reference position specified by origin. The End-of-File internal indicator of the file is cleared after a call to this function.

Return Value: If successful, the function returns a zero value. Otherwise, it returns nonzero value.

#include<stdio.h>int main () {FILE * fp; fp = fopen ( "myfile.txt" , "w" );fputs ( "This is an apple." , fp ); fseek ( fp , -8 , SEEK_END );fputs ( " sam" , fp ); fclose ( fp );return 0; }
Got questions? Get instant answers now!

After this code is successfully executed, the file myfile.txt contains:

This is a sample.
#include<stdio.h>int main () {FILE * fp; fp = fopen ( "myfile.txt" , "w" );fputs ( "This is an apple." , fp ); fseek ( fp , 9 , SEEK_SET );fputs ( " sam" , fp ); fclose ( fp );return 0; }
Got questions? Get instant answers now!

After this code is successfully executed, the file myfile.txt contains:

This is a sample.

Rewind() function

void rewind (FILE *fp);

This function sets the current position indicator associated with fp to the beginning of the file. A call to rewind is equivalent to:

fseek (fp, 0, SEEK_SET);

except that, unlike fseek, rewind clears the error indicator.

On streams open for update (read+write), a call to rewind allows to switch between reading and writing.

#include<stdio.h>#include<conio.h>int main () {char str [80];int n; FILE * fp;fp = fopen ("myfile.txt","w+"); for ( n='A' ; n<='Z' ; n++) fputc ( n, fp);rewind (fp); n=0;while (!feof(fp)) {str[n]= fgetc(fp);n++; }fclose (fp); printf ("I have read: %s \n",str);getch(); return 0;}
Got questions? Get instant answers now!

A file called myfile.txt is created for reading and writing and filled with the alphabet. The file is then rewinded, read and its content is stored in a buffer, that then is written to the standard output:

Questions & Answers

What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Introduction to computer science. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10776/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Introduction to computer science' conversation and receive update notifications?

Ask