//读写切换必须fseek

struct sRead,sWrite;

FILE *fp = fopen(...);

if(fp)

{

while(fread(&sRead,sizeof(sRead),1,fp) != feof)

{

//读写切换必须fseek

fseek(fp,-sizeof(sRead),SEEK_CUR);

fwrite(&sWrite,sizeof(sWrite),1,fp);

//读写切换必须fseek

fseek(fp,0L,SEEK_CUR);

}

}