|
LL){
return EOF;
}
}
f->ptr = f->base;
int n = read(f->fd,f->ptr,BUFSIZ); //系统调用read
if(n == 0){ //到达文件结尾
f->base = NULL;
f->cnt = 0;
f-> flag |= _EOF;
return EOF;
}else if(n == -1){ //出错
f->cnt= 0;
f->flag |= _ERR;
return EOF;
}else{
f->cnt = --n;
return *f->ptr++;
}
}
int _flushbuf(int x,FILE *f){
if((f->flag & (_WRITE | _EOF | _ERR)) != _WRITE){
return EOF;
}
int n;
int bufsize = f->flag & _UNBUF ? 1 : BUFSIZ;
if(f->base != NULL){
n = write(f->fd,f->base,f->ptr - f->base); //判断需要写入多少字节
if(n != f->ptr - f->base){
f->flag |= _ERR;
return EOF;
}
}else{
if((f->base = (char *)malloc(bufsize)) == NULL){
f->flag |= _ERR;
return EOF;
}
}
if(x != EOF){
f->cnt = bufsize - 1;
f->ptr = f->base;
*f->ptr++ = x;
}else{ //当写入EOF时，代表强制刷新缓冲区内容到文件中
f->cnt = bufsize;
f->ptr = f->base;
}
return x;
}
/**
* @brief _fflush
* @param f
* @return
*/
int _fflush(FILE *f){
int res = 0;
if(f == NULL){
for(int i = 0; i < OPEN_MAX; i++){ //当参数为NULL时，刷新所有的文件流
if((f->flag & _WRITE) && (_fflush(&_iob[i]) == -1)){ //有一个出错即返回-1
res = EOF;
}
}
}else{
if(f->flag & _WRITE){
_flushbuf(EOF,f);
}else{
res = EOF;
}
}
if(f->flag & _ERR){ //出错
res = EOF;
}
return res;
}
int _fclose(FILE *f){
int ret;
if((ret = _fflush(f)) != EOF){
free(f->base);
f->base = NULL;
f->ptr = NULL;
f->fd = 0;
f->flag = 0; //@TODO
}
return 0;
}
int _fseek(FILE *f,long offset,int origin){
int rc;
if(f->flag & _READ) {
if(origin == 1) {
offset -= f->cnt;
}
rc = lseek(f->fd,offset,origin);
f->cnt = 0; //将缓冲区剩余字符数清0
}else if(f->flag & _WRITE) {
rc = _fflush(f); //强制刷新缓冲区
if(rc != EOF) {
rc = lseek(f->fd,offset,origin);
}
}
return rc == -1 ? EOF : 0;
}
int _getc(FILE *f){
return --f->cnt >= 0 ? *f->ptr++ : _fillbuf(f);
}
int _putc(int x,FILE *f){
return --f->cnt >= 0 ? *f->ptr++ = x : _flushbuf(x,f);
}
int _getchar(){
return _getc(stdin);
}
int _putchar(int x){
return _putc(x,stdout);
}
FILE *_fopen(char *file,char *mode){
int fd;
FILE *fp;
if(*mode != 'r' && *mode != 'w' && *mode != 'a') {
return NULL;
}
for(fp = _iob; fp < _iob + OPEN_MAX; fp++) { //寻找一个空闲位置
if (fp->flag == 0){
break;
}
}
if(fp >= _iob + OPEN_MAX){
return NULL;
}
if(*mode == 'w'){
fd = creat(file,PERMS);
}else if(*mode == 'r'){
fd = open(file,O_RDONLY,0);
}else{ //a模式
if((fd = open(file,O_WRONLY,0)) == -1){
fd = creat(file,PERMS);
}
lseek(fd,0L,2); //文件指针指向末尾
}
if(fd == -1){
return NULL;
}
fp->fd = fd;
fp->cnt = 0; //fopen不分配缓存空间
fp->base = NULL;
fp->ptr = NULL;
fp->flag = *mode == 'r' ? _READ : _WRITE;
return fp;
}
int main(int argc,char *argv[]){
FILE *f = _fopen("zyc.txt","a");
/*char c;
for(int i = 0; i < 10; i++){
c = _getc(f);
}*/
/*for(int i = 0; i < 9; i++){
_putc('6',f);
}
_fseek(f,-5,1);
for(int i = 0; i < 9; i++){
_putc('8',f);
}
_fclose(f);*/
int c;
while((c = _getchar()) != '\n'){
_putchar(c);
}
_fclose(stdout);
return 0;
}
上面提到的部分函数在Answer to Exercise 8-3, page 179中有更详细的实现。
参考资料：
|