Descriptions:
Develop a program that uses mmap() to map a file to memory space. Prepare such a file by yourself and do the follows.
- <LI class=MsoNormal>Display the content of the file after mapping; <LI class=MsoNormal>Output how many digits included in the file; <LI class=MsoNormal>Replace all the digits with �*';
- Display the content after making the changes.
#include<stdio.h>
#include<sys/types.h>
#include<sys/mman.h>
#include<stdlib.h>
#include<fcntl.h>
#include<sys/stat.h>
#include<unistd.h>
#include<signal.h>
#include<string.h>
main(int argc, char *argv[])
{
int fd,changes,i,random_spot,kids[2];
struct stat buf;
char *the_file,*starting_string="using mmap() can be fun\nand informative!";
if (argc!=3)
{
fprintf(stderr, "Usage %s file_name #_of_changes\n",*argv);
exit(1);
}
if((changes=atoi(argv[2]))<1)
{
fprintf(stderr,"# of changes<1 \n");
exit(2);
}
if((fd=open(argv[1], O_CREAT | O_RDWR,0666))<0)
{
fprintf(stderr,"open error on file %s\n",*argv);
exit(3);
}
write(fd,starting_string,strlen(starting_string));
if(fstat(fd,&buf)<0)
{
fprintf(stderr,"fstat error on file %s\n",argv);
exit(4);
}
if((the_file=mmap(0,(size_t)
buf.st_size,PROT_READ|PROT_WRITE,MAP_SHARED,fd,0))==(caddr_t)-1)
{
fprintf(stderr,"mmap failure\n");
exit(5);
}
for(i=0;i<2;++i)
if((kids[i]=(int)fork())==0)
while(1)
{
printf("Child %d finds:\n%s\n",getpid(),the_file);
sleep(1);
}
srand((unsigned) getpid());
for(i=0;i<changes;++i)
{
random_spot=(int)(rand()%buf.st_size);
*(the_file+random_spot)='';
sleep(1);
}
printf("Parent done with changes\n");
for(i=0;i<2;++i)
kill(kids[i],9);
printf("The file now contains:\n%s\n",the_file);
exit(0);
}
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