Linux程序设计-mmap使用

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#include <unistd.h>#include <stdio.h>#include <stdlib.h>#include <sys/mman.h>#include <fcntl.h>typedef struct {    int integer;    char string[24];} RECORD;#define NRECORDS (100)int main(){    RECORD record, *mapped;    int i, f;    FILE *fp;//---------------------------------------------------------------------//往文件中写入结构体即: RECORD-%0 到 RECORD-%99//---------------------------------------------------------------------    fp = fopen("records.dat","w+");     for(i=0; i<NRECORDS; i++) {        record.integer = i;        sprintf(record.string,"RECORD-%d",i);        fwrite(&record,sizeof(record),1,fp);    }    fclose(fp);//---------------------------------------------------------------------//从文件中读出结构体record,并为其赋值再写到文件去.//向后移动43个,下标从0开始正好是第43个//---------------------------------------------------------------------    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);//把f指向文件0地址开始大小为NRECORDS*sizeof(record)映射到内存处，返回内存起始地址//---------------------------------------------------------------------//把文件映射到内存去,并改变内存中其值,等于就是在改变文件中的内容的!!//---------------------------------------------------------------------    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);//实现磁盘文件内容与共享内存区中的内容一致,即同步操作    msync((void *)mapped, NRECORDS*sizeof(record), MS_ASYNC);    munmap((void *)mapped, NRECORDS*sizeof(record));    close(f);    exit(0);}
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