mmap函数的用法 |
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[plain]
mmap函数的用法 (2005-11-06 09:14)
分类： C/C++
改自Wrox《Linux程序设计》
#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)
int main()
{
RECORD record, *mapped;
int i, f;
FILE *fp;
fp = fopen("records.dat", "w+");
for (i = 0; i < NRECORDS; i++)
{
memset(&record, 0, sizeof(record));/* 若不清空，内容未知 */
record.integer = i;
sprintf(record.string, "RECORD-%d", i);
fwrite(&record,sizeof(record), 1, fp);
}
fclose(fp);
/* 修改43条记录 */
fp = fopen("records.dat", "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);
/* 修改43条记录 */
f = open("records.dat", O_RDWR);
mapped = (RECORD *)mmap(0, NRECORDS*sizeof(record),
PROT_READ|PROT_WRITE, MAP_SHARED, f, 0);
mapped[43].integer = 243;
sprintf(mapped[43].string, "RECORD-%d", mapped[43].integer);
msync((void *)mapped,NRECORDS*sizeof(record), MS_ASYNC);
munmap((void *)mapped,NRECORDS*sizeof(record));
close(f);
return 0;
}
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