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#include <unistd.h>
#include <stdio.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <stdlib.h>
typedef struct
{
int integer;
char string[24];
} RECORD;
#define NRECORDS 100
#define FILENAME ("records.dat")
int main()
{
RECORD record, *mapped;
int i,f;
FILE *fp;
fp = fopen(FILENAME,"w+");
if(!fp)
{
perror("opern file error");
return EXIT_FAILURE;
}
for(i = 0; i < NRECORDS; i++)
{
bzero(&record,sizeof(record));
record.integer = i;
sprintf(record.string,"RECORD-%d",i);
fwrite(&record,sizeof(record),1,fp);
}
fclose(fp);
fp = fopen(FILENAME,"r+");
fseek(fp,43*sizeof(record),SEEK_SET);
fread(&record,sizeof(record),1,fp);
record.integer = 143;
sprintf(record.string,"RECORD-%d",record.integer);
fseek(fp,43*sizeof(record),SEEK_SET);
fwrite(&record,sizeof(record),1,fp);
fclose(fp);
//´ò¿ªÎļþ,¿É¶Á¿Éд
f = open(FILENAME,O_RDWR);
//ÒÔ¹²Ïíģʽmmap£¬Ïê¼ûman mmap
mapped = (RECORD *)mmap(0,NRECORDS * sizeof(record),
PROT_READ | PROT_WRITE,MAP_SHARED,f,0);
//¸Ä±äÆäÖеÄÖµ£¬×Ö·û´®ºÍÊýÖµ
mapped[43].integer = 243;
sprintf(mapped[43].string,"RECORD-%d",mapped[43].integer);
//д»ØÎļþ£¬×îºóÒ»¸ö²ÎÊýÖ¸¶¨ÁËͬ²½¡¢Òì²½¡¢»Ø´«
msync((void *)mapped,NRECORDS * sizeof(record),MS_ASYNC)


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תÔØ:Hadoop Ó¦¸ÃÓÃC++ʵÏÖ£¬¶ø²»ÊÇJava

http://www.trendcaller.com/2009/05/hadoop-should-target-cllvm-not-java.html
Sunday, May 10, 2009
Hadoop should target C++/LLVM, not Java (because of watts)
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¸ßÖÊÁ¿C++/C±à³ÌÖ¸ÄÏ ÄÚ´æ¹ÜÀí

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640K ought to be enough for everybody
— Bill Gates 1981
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C/C++Êý¾ÝÀàÐÍ(ÍøÉÏ×ÊÁÏ×ܽá)

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