p10-11.c

SUN Solaris8平台下进程间通信

#include <unistd.h>
#include <stdio.h>
#include <sys/mman.h>
#define NRECORDS (100)
typedef struct {
    int integer;
    char string[24];
} RECORD;
int main(void)
{
    RECORD record, *mapped;
    int i,f;
    FILE *fp;
    fp = fopen("records.dat","w+");
    /* 写记录至文件 */
    for (i=0;i<NRECORDS;i++){
        record.integer = i;
        sprintf(record.string, "RECORD-%d", i);
        fwrite(&record,sizeof(record),1,fp);
    }
    fclose(fp);
    /* 重新打开此文件用通常的方法修改第43个记录 */
    fp = fopen("records.dat","r+");
    fseek(fp, 43*sizeof(record), SEEK_SET);  /* 定位文件位置于第43个记录处 */
    fread(&record, sizeof(record),1, fp);    /* 读出该记录 */
    record.integer = 143;                    /* 修改记录号 */
    sprintf(record.string, "RECORD-%d",record.integer);
    fseek(fp,43*sizeof(record),SEEK_SET);    /* 再次定位文件位置于第43个记录处 */
    fwrite(&record,sizeof(record),1,fp);     /* 将修改后的记录写回文件 */
    fclose(fp);
    /* 重新打开此文件用存储映射方法修改第43个记录 */
     f = open("records.dat",O_RDWR);
    /* 将文件的前NRECORDS个记录映射到内存 */
    mapped = (RECORD *)mmap(0, NRECORDS*sizeof(record),
                  PROT_READ|PROT_WRITE,MAP_SHARED, f, 0);
    mapped[43].integer = 243;     /* 修改第43个记录的记录号 */
    sprintf(mapped[43].string, "RECORD-%d",mapped[43].integer);
    msync((void*)mapped, NRECORDS*sizeof(record), MS_ASYNC);
    munmap((void*)mapped, NRECORDS*sizeof(record)); /* 删除存储映射 */
    /*查看文件有否改变 */ 
    lseek(f, 43*sizeof(record), SEEK_SET);
    read(f, &record, sizeof(record));
    printf("record[43].integer = %d\n",record.integer);
    close(f);
    exit(0);
}