Linux under C programming-----io/file operation/memory mapping for simple record storage (3)

Using the file memory mapping under Linux can realize the process sharing data, we can map a file to virtual memory to enable multiple processes to share,

We can probably think of a wide range of areas that he can apply to here.

It mainly involves the application of three functions of Mmap Munmap Msync

Paste the following code

The following code establishes a simple record store for a file and modifies the contents of the file through a memory map

/*************************************************************************> File name:memdb.c> Author: > Mail: > Created time:fri 03:46:11 AM PST **************************************************************** /#include <stdio.h> #include <sys/mman.h> #include <stdlib.h> #include <string.h># include<unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #define   Record_num 100#define data_file "./db.dat"//define data record typedef struct {int index; Char str[20];}    Recorddata;int Main () {file*pfile;    Void*pmap=null;    int fdfile;    int i;      RecordData Record,*pmappedrecord;    Pfile=fopen (data_file, "w+");        if (pfile==null) {printf ("Create File error\n");    return 0;      } for (i=0;i<record_num;i++) {record.index=i;      sprintf (Record.str, "record:%d", I);   Fwrite (void*) &record,sizeof (record), 1,pfile);   } fclose (PFile);   Fdfile =open (DATA_FILE,O_RDWR); if (fdfile==-1) {printf ("Open datafile error!\n");    return 0; }//map file to memory from the file offset 0 to end Pmap=mmap (null,sizeof (recorddata) *record_num,prot_read|    prot_write,map_shared,fdfile,0);        if (pmap==map_failed) {printf ("MAP file to Virtual Memory error!\n");        Close (Fdfile);    return 0;    }///get thirty record pmappedrecord= (struct recorddata*) PMap;        printf ("%d:%s\n", pmappedrecord[29].index,pmappedrecord[29].str);    Modify thirty data sprintf (PMAPPEDRECORD[29].STR, "%s", "Hello,usher");    Update mapped memory info to file Msync (pmap,sizeof (recorddata) *record_num,ms_async); Munmap (pmap,sizeof (recorddata) *record_num);}

<span Style= "Font-family:arial, Helvetica, Sans-serif; font-size:12px; " > We can view the contents of shared files in another process </span> 

</pre><pre code_snippet_id= "604510" snippet_file_name= "blog_20150213_6_8975773" name= "code" class= "CPP" >/*************************************************************************> File name:memdb.c> Author: > Mail: > Created time:fri 03:46:11 AM PST ************************************************************ /#include <stdio.h> #include <sys/mman.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #define   Record_num 100#define data_file "./db.dat"//define data record typedef struct {int index; Char str[20];}    Recorddata;int Main () {int i;    Void*pmap=null;    int fdfile;     RecordData Record,*pmappedrecord;    Fdfile =open (DATA_FILE,O_RDWR);        if (fdfile==-1) {printf ("Open datafile error!\n");    return 0; }//map file to memory from the file offset 0 to end Pmap=mmap (null,sizeof (recorddata) *record_num,prot_read|    prot_write,map_shared,fdfile,0);        if (pmap==map_failed) {printf ("MAP file to Virtual Memory error!\n");        Close (Fdfile);    return 0;    }///get thirty record pmappedrecord= (struct recorddata*) PMap;         for (i=0;i<record_num;i++) printf ("%d:%s\n", pmappedrecord[i].index,pmappedrecord[i].str); Munmap (pmap,sizeof (recorddata) *record_num);}

Linux under C programming-----io/file operation/memory mapping for simple record storage (3)