说明：这个例子是采用共享文件映射形式，写端写入数据，读端读取数据。
写端：
/*-------------map_normalfile1.c-----------*/
#include <sys/mman.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
typedef struct{
char name[4];
int age;
}people;
main(int argc, char** argv) // map a normal file as shared mem:
{
int fd,i;
people *p_map;
char temp;
//open file
fd=open(argv[1],O_CREAT|O_RDWR|O_TRUNC,00777);
printf("file opened\n");
/* man open
NAME
open, openat - open a file
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int open(const char *path, int oflag, mode_t mode ...);
DESCRIPTION
The open() function establishes the connection between a
file and a file descriptor. It creates an open file descrip-
tion that refers to a file and a file descriptor that refers
to that open file description. The file descriptor is used
by other I/O functions to refer to that file. The path
argument points to a pathname naming the file.
The file offset used to mark the current position within the
file is set to the beginning of the file.
The file status flags and file access modes of the open file
description are set according to the value of oflag. The
mode argument is used only when O_CREAT is specified (see
below.)
Values for oflag are constructed by a bitwise-inclusive-OR
of flags from the following list, defined in <fcntl.h>.
Applications must specify exactly one of the first three
values (file access modes) below in the value of oflag:
O_RDONLY
Open for reading only.
O_WRONLY
Open for writing only.
O_RDWR
Open for reading and writing. The result is undefined
if this flag is applied to a FIFO.
Any combination of the following may be used:
O_APPEND
If set, the file offset is set to the end of the file
prior to each write.
O_CREAT
Create the file if it does not exist. This flag
requires that the mode argument be specified.
.....
*/
lseek(fd,sizeof(people)*5-1,SEEK_SET);
write(fd,"",1);
/*
NAME
lseek - move read/write file pointer
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
off_t lseek(int fildes, off_t offset, int whence);
DESCRIPTION
The lseek() function sets the file pointer associated with
the open file descriptor specified by fildes as follows:
o If whence is SEEK_SET, the pointer is set to offset
bytes.
o If whence is SEEK_CUR, the pointer is set to its
current location plus offset.
o If whence is SEEK_END, the pointer is set to the size
of the file plus offset.
The symbolic constants SEEK_SET, SEEK_CUR, and SEEK_END are
defined in the header <unistd.h>.
*/
//create mmap
p_map = (people*) mmap(NULL, sizeof(people)*100, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
close( fd );
/*
NAME
mmap - map pages of memory
SYNOPSIS
#include <sys/mman.h>
void *mmap(void *addr, size_t len, int prot, int flags, int
fildes, off_t off);
DESCRIPTION
The mmap() function establishes a mapping between a
process's address space and a file or shared memory object.
The format of the call is as follows:
pa = mmap(addr, len, prot, flags, fildes, off);
The mmap() function establishes a mapping between the
address space of the process at an address pa for len bytes
to the memory object represented by the file descriptor
fildes at offset off for len bytes. The value of pa is a
function of the addr argument and values of flags, further
described below. A successful mmap() call returns pa as its
result. The address range starting at pa and continuing for
len bytes will be legitimate for the possible (not neces-
sarily current) address space of the process. The range of
bytes starting at off and continuing for len bytes will be
legitimate for the possible (not necessarily current)
offsets in the file or shared memory object represented by
fildes.
*/
//write mmap
temp = 'a';
for(i=0; i<100; i++)
{
temp += 1;
memcpy(( *(p_map+i)).name, &temp, 2);
(*(p_map+i)).age = 20+i;
}
printf("initialize over\n");
//unmap the mmap
sleep(10);
munmap((char*)p_map, sizeof(people)*100);
printf("umap ok\n");
/*
NAME
munmap - unmap pages of memory
SYNOPSIS
#include <sys/mman.h>
int munmap(void *addr, size_t len);
DESCRIPTION
The munmap() function removes the mappings for pages in the
range [addr, addr + len), rounding the len argument up to
the next multiple of the page size as returned by
sysconf(3C). If addr is not the address of a mapping esta-
blished by a prior call to mmap(2), the behavior is unde-
fined. After a successful call to munmap() and before any
subsequent mapping of the unmapped pages, further references
to these pages will result in the delivery of a SIGBUS or
SIGSEGV signal to the process.
*/
}
读端：
/*-------------map_normalfile2.c-----------*/
#include <sys/mman.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
typedef struct{
char name[4];
int age;
}people;
main(int argc, char** argv) // map a normal file as shared mem:
{
int fd,i;
people *p_map;
//open file
fd=open( argv[1],O_CREAT|O_RDWR,00777 );
//create mmap and read
p_map = (people*)mmap(NULL,sizeof(people)*100, PROT_READ|PROT_WRITE, MAP_SHARED,fd,0);
for(i = 0;i<100;i++)
{
printf( "name: %s age %d;\n",(*(p_map+i)).name, (*(p_map+i)).age );
}
//unmap
munmap((char*)p_map,sizeof(people)*100);
}