C Program to lock file using semaphores.

Write a C Program to lock file using semaphores.
Using semaphores, We can control access to files, shared memory and other things. The basic functionality of a semaphore is that you can either set it, check it, or wait until it clears then set it (“test-n-set”). In C semaphores functions defined in the sys/sem library. Read more about C Programming Language . and read the C Programming Language (2nd Edition) by K and R.

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#include <stdio.h>
#include <sys/file.h>
#include <error.h>
#include <sys/sem.h>
#define MAXBUF 100
#define KEY 1216
#define SEQFILE "seq_file"
int semid,fd;
void my_lock(int);
void my_unlock(int);
union semnum
{
int val;
struct semid_ds *buf;
short *array;
}arg;
int main()
{
int child, i,n, pid, seqno;
char buff[MAXBUF+1];
pid=getpid();
if((semid=semget(KEY, 1, IPC_CREAT | 0666))= = -1)
{
perror("semget");
exit(1);
}
arg.val=1;
if(semctl(semid,0,SETVAL,arg)<0)
perror("semctl");
if((fd=open(SEQFILE,2))<0)
{
perror("open");
exit(1);
}
pid=getpid();
for(i=0;i<2;i++)
{
my_lock(fd);
lseek(fd,01,0);
if((n=read(fd,buff,MAXBUF))<0)
{
perror("read");
exit(1);
}
printf("pid:%d, Seq no:%dn", pid, seqno);
seqno++;
sprintf(buff,"%dn", seqno);
n=strlen(buff);
lseek(fd,01,0);
if(write(fd,buff,n)!=n)
{
perror("write");
exit(1);
}
sleep(1);
my_unlock(fd);
}
}
void my_lock(int fd)
{
struct sembuff sbuf=(0, -1, 0);
if(semop(semid, &sbuf, 1)= =0)
printf("Locking: Resource…n");
else
printf("Error in Lockn");
}
void my_unlock(int fd)
{
struct sembuff sbuf=(0, 1, 0);
if(semop(semid, &sbuf, 1)= =0)
printf("UnLocking: Resource…n");
else
printf("Error in Unlockn");
}
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C Program to find the size of a given file.

Write a C Program to find the size of a given file.
The function fseek() is used to set the file pointer at the specified position. In general, it is used to move the file pointer to the desired position within the file.
In this program we moved the file pointer to the end of file, and obtain the current position of the file pointer. Function rewind() also moves the file pointer to the beginning of the file, but syntax and number of parameters are different. Read more about C Programming Language .

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*
* Happy Coding
***********************************************************/


#include<stdio.h>
#include<process.h>
long file_size(FILE *fp)
{
long len;
//move file pointer to end of the file */
fseek(fp, 0L, 2);
//Obtain the current position of file pointer
len = ftell(fp);
return len;
}
void main(void)
{
FILE *fp;
char filename[20];
printf("nEnter the file name:nn");
scanf("%s",filename);

fp = fopen(filename, r);

if(fp == NULL)
{
printf("Error: file not found!nn");
exit(0);
}
printf("File size of %s is %ld bytesnn",filename, file_size(fp));
fclose(fp);
}

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K & R C Programs Exercise 7-8.

K and R C, Solution to Exercise 7-8:
K and R C Programs Exercises provides the solution to all the exercises in the C Programming Language (2nd Edition). You can learn and solve K&R C Programs Exercise.
C Program to print a set of files, starting each new one on a new page, with a title and running page for each file Read more about C Programming Language .

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* You can use all the programs on www.c-program-example.com
* for personal and learning purposes. For permissions to use the
* programs for commercial purposes,
* contact info@c-program-example.com
* To find more C programs, do visit www.c-program-example.com
* and browse!
*
* Happy Coding
***********************************************************/

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

#define MAXBOT 3
#define MAXHDR 5
#define MAXLINE 100
#define MAXPAGE 66

/*print: print files - each new one on a new page */
main(int argc, char *argv[])
{

FILE *fp;
void fileprint(FILE *fp, char *fname);

if(argc == 1)
fileprint(stdin," ");
else
if((fp = fopen(*++argv,"r")) == NULL) {
fprintf(stderr,"find:can't open %sn",*argv);
exit(1);
} else {

fileprint(fp, *argv);
fclose(fp);
}
return 0;
}


//fileprint: print file name
void fileprint(FILE *fp, char *fname)
{
int lineno, pageno = 1;
char line[MAXLINE];
int heading(char *fname, int pageno);
lineno = heading(fname, pageno++);
while(fgets(line, MAXLINE, fp) != NULL) {
if(lineno == 1) {
fprintf(stdout,"f");
lineno = heading(fname, pageno++);
}
fputs(line, stdout);
if(++lineno > MAXPAGE - MAXBOT)
lineno = 1;
}
fprintf(stdout,"f");
}

//heading: put heading and enough blank lines
int heading(char *fname, int pageno)
{
int ln = 3;
fprintf(stdout,"nn");
fprintf(stdout,"%s page %dn", fname, pageno);
while(ln++ < MAXHDR)
fprintf(stdout,"n");
return ln;
}
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K & R C Programs Exercise 7-6.

K and R C, Solution to Exercise 7-6:
K and R C Programs Exercises provides the solution to all the exercises in the C Programming Language (2nd Edition). You can learn and solve K&R C Programs Exercise.
Write a C Program to compare two files, printing the first line where they differ.
Read more about C Programming Language .

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***********************************************************/

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

#define MAXLINE 100
/*comp: compare two file, printing the first line where they differ*/
main(int argc, char *argv[])
{
FILE *fp1, *fp2;
void filecomp(FILE *fp1, FILE *fp2);
if(argc != 3){
fprintf(stderr,"comp:need two file namesn");
exit(1);
} else {
if((fp1 = fopen(*++argv, "r")) == NULL) {
fprintf(stderr, "comp:can't open %sn",*argv);
exit(1);
} else if((fp2 = fopen(*++argv, "r")) == NULL) {
fprintf(stderr, "comp:can't open %sn",*argv);
exit(1);
}else {
filecomp(fp1,fp2);
fclose(fp1);
fclose(fp2);
exit(0);

}
}
}

//filecomp: compare two files -a line at a time
void filecomp (FILE *fp1, FILE *fp2)
{
char line1[MAXLINE], line2[MAXLINE];
char *lp1 = *lp2;
do{
lp1 = fgets(line1, MAXLINE, fp1);
lp2 = fgets(line2, MAXLINE, fp2);
if(lp1 == line1 && lp2 == line2){

if(strcmp(line1,line2) !=0) {
printf("First difference in linen%sn",line1);
lp1 = lp2 = NULL;
}
} else if(lp1 != line1 && lp2 == line2)
printf("end of first file at linen%sn",line2);
else if(lp1 == line1 && lp2 == line2)
printf("end of second file at line n%sn",line1);

}while(lp1 == line1 && lp2 == line2);
}



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C Program which produces its own source code as its output.

Write a c program which produces its own source code as its output.
This C program uses the C File i/o operations like fopen(), fclose(). In this program, We pritn the source code of the program.Read more about C Programming Language .

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* and browse!
*
* Happy Coding
***********************************************************/

#include<stdio.h>
int main()
{
FILE *fp;
char c;

fp = fopen(__FILE__,"r");

do{

c= getc(fp);

putchar(c);

}
while(c!=EOF);

fclose(fp);

return 0;

}


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C Program to count number of characters in the file

C Program to count number of characters in the file. In this program you can learn c file operations. Here we counting the characters by reading the characters in the file one by one and if read character was not an ‘n’ ,’t’ or EOF, it increments the counter by one. Read more about C Programming Language .

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* programs for commercial purposes,
* contact info@c-program-example.com
* To find more C programs, do visit www.c-program-example.com
* and browse!
*
* Happy Coding
***********************************************************/

#include<stdio.h>
#include<conio.h>

void main()
{
char ch;
int count=0;
FILE *fptr;
clrscr();
fptr=fopen("text.txt","w");
if(fptr==NULL)
{
printf("File can't be createda");
getch();
exit(0);
}
printf("Enter some text and press enter key:n");
while((ch=getche())!='r')
{
fputc(ch,fptr);
}
fclose(fptr);
fptr=fopen("text.txt","r");
printf("nContents of the File is:");
while((ch=fgetc(fptr))!=EOF)
{
count++;
printf("%c",ch);
}
fclose(fptr);
printf("nThe number of characters present in file is: %d",count);
getch();
}

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C Program to demonstrate the ‘fgets’ function.

Program to demonstrate the ‘fgets’ function. The program will count the number of lines in a file. This is a function of the UNIX command ‘wc’. Read more about C Programming Language .

/***********************************************************
* You can use all the programs on www.c-program-example.com
* for personal and learning purposes. For permissions to use the
* programs for commercial purposes,
* contact info@c-program-example.com
* To find more C programs, do visit www.c-program-example.com
* and browse!
*
* Happy Coding
***********************************************************/



#include <stdio.h>

#define LINE_LENGTH 80

main()
{
FILE* fp;
char line[LINE_LENGTH];
int count=0;

fp=fopen("/home/DOC/C/c.html","r");
/* Count up the lines here. */
while ( fgets(line, LINE_LENGTH, fp) != NULL) count++;

printf("File contains %d lines.n", count);

fclose(fp);
}
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C Program to reverse the first n characters in a file.

C Program to reverse the first n characters in a file using the command line arguments. Here we read the file name and n are specified on the command line. If file exists, it reverse the n characters, else it gives the error message. Read more about C Programming Language .

/***********************************************************
* You can use all the programs on www.c-program-example.com
* for personal and learning purposes. For permissions to use the
* programs for commercial purposes,
* contact info@c-program-example.com
* To find more C programs, do visit www.c-program-example.com
* and browse!
*
* Happy Coding
***********************************************************/


#include <stdio.h>
#include <conio.h>
#include <string.h>
#include <process.h>

void main(int argc, char *argv[])
{
char a[15];
char s[20];
char n;
int k;
int j=0;
int i;
int len;
FILE *fp;

if(argc!=3)
{
puts("Improper number of arguments.");
exit(0);
}
fp = fopen(argv[1],"r");
if(fp == NULL)
{
puts("File cannot be opened.");
exit(0);
}

k=*argv[2]-48;
n = fread(a,1,k,fp);
a[n]='';
len=strlen(a);
for(i=len-1;i>=0;i--)
{
s[j]=a[i];
printf("%c",s[j]);
j=j+1;
}
s[j+1]='';
getch();
}/*(Note: The file name and n are specified on the command line.)*/

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C program which copies one file contents to another file.

C Program which copies one file contents to another file. Here we read the one file and copies the characters to another file which are existed in the disc. Here we read the file names from the command line.Read more about C Programming Language .

/***********************************************************
* You can use all the programs on www.c-program-example.com
* for personal and learning purposes. For permissions to use the
* programs for commercial purposes,
* contact info@c-program-example.com
* To find more C programs, do visit www.c-program-example.com
* and browse!
*
* Happy Coding
***********************************************************/



#include <stdio.h>
#include <conio.h>
#include <process.h>

void main(int argc, char *argv[])
{
FILE *fs,*ft;
char ch;
clrscr();
if(argc!=3)
{
puts("Invalid number of arguments.");
exit(0);
}
fs = fopen(argv[1],"r");
if(fs==NULL)
{
puts("Source file cannot be opened.");
exit(0);
}
ft = fopen(argv[2],"w");
if (ft==NULL)
{
puts("Target file cannot be opened.");
fclose(fs);
exit(0);
}
while(1)
{
ch=fgetc(fs);
if (ch==EOF)
break;
else
fputc(ch,ft);
}
fclose(fs);
fclose(ft);
getch();
}

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C Program to do the operations of Sequential file with records.

C Program to do the operations of Sequential file with records. Sequential file, A file which consists of the same record types that is stored on a secondary storage device. The physical sequence of records may be based upon sorting values of one or more data items or fields. Here we are creating, Reading, searching the sequential file, using c file i/o operations. Read more about C Programming Language .

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* programs for commercial purposes,
* contact info@c-program-example.com
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*
* Happy Coding
***********************************************************/


#include <stdio.h>
typedef struct
{
int usn;
char name[25];
int m1,m2,m3;
}STD;

STD s;

void display(FILE *);
int search(FILE *,int);

void main()
{
int i,n,usn_key,opn;
FILE *fp;
printf(" How many Records ? ");
scanf("%d",&n);
fp=fopen("stud.dat","w");
for(i=0;i<n;i++)
{
printf("Read the Info for Student: %d (usn,name,m1,m2,m3) n",i+1);
scanf("%d%s%d%d%d",&s.usn,s.name,&s.m1,&s.m2,&s.m3);
fwrite(&s,sizeof(s),1,fp);
}
fclose(fp);
fp=fopen("stud.dat","r");
do
{
printf("Press 1- Displayt 2- Searcht 3- Exitt Your Option?");
scanf("%d",&opn);
switch(opn)
{
case 1: printf("n Student Records in the File n");
display(fp);
break;
case 2: printf(" Read the USN of the student to be searched ?");
scanf("%d",&usn_key);
if(search(fp,usn_key))
{
printf("Success ! Record found in the filen");
printf("%dt%st%dt%dt%dn",s.usn,s.name,s.m1,s.m2,s.m3);
}
else
printf(" Failure!! Record with USN %d not foundn",usn_key);
break;
case 3: printf(" Exit!! Press a key . . .");
getch();
break;
default: printf(" Invalid Option!!! Try again !!!n");
break;
}
}while(opn != 3);
fclose(fp);
} /* End of main() */

void display(FILE *fp)
{
rewind(fp);
while(fread(&s,sizeof(s),1,fp))
printf("%dt%st%dt%dt%dn",s.usn,s.name,s.m1,s.m2,s.m3);
}
int search(FILE *fp, int usn_key)
{
rewind(fp);
while(fread(&s,sizeof(s),1,fp))
if( s.usn == usn_key) return 1;
return 0;
}





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