FATFS 初学之 f

FATFS 初学之 f_truncate

 1 /*-----------------------------------------------------------------------*/
 2 /* Truncate File                                                         */
 3 /*-----------------------------------------------------------------------*/
 4 
 5 FRESULT f_truncate (
 6     FIL *fp        /* Pointer to the file object */
 7 )
 8 {
 9     FRESULT res;
10     DWORD ncl;
11 
12 
13     res = validate(fp->fs, fp->id);        /* Check validity of the object */
14     if (res == FR_OK) {
15         if (fp->flag & FA__ERROR) {            /* Check abort flag */
16             res = FR_INT_ERR;
17         } else {
18             if (!(fp->flag & FA_WRITE))        /* Check access mode */
19                 res = FR_DENIED;
20         }
21     }
22     if (res == FR_OK) {
23         if (fp->fsize > fp->fptr) {
24             fp->fsize = fp->fptr;    /* Set file size to current R/W point */
25             fp->flag |= FA__WRITTEN;
26             if (fp->fptr == 0) {    /* When set file size to zero, remove entire cluster chain */
27                 res = remove_chain(fp->fs, fp->sclust);
28                 fp->sclust = 0;
29             } else {                /* When truncate a part of the file, remove remaining clusters */
30                 ncl = get_fat(fp->fs, fp->clust);
31                 res = FR_OK;
32                 if (ncl == 0xFFFFFFFF) res = FR_DISK_ERR;
33                 if (ncl == 1) res = FR_INT_ERR;
34                 if (res == FR_OK && ncl < fp->fs->n_fatent) {
35                     res = put_fat(fp->fs, fp->clust, 0x0FFFFFFF);
36                     if (res == FR_OK) res = remove_chain(fp->fs, ncl);
37                 }
38             }
39         }
40         if (res != FR_OK) fp->flag |= FA__ERROR;
41     }
42 
43     LEAVE_FF(fp->fs, res);
44 }

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函数功能：截断文件大小

描述：

f_truncate函数当 _FS_READONLY == 0 并且 _FS_MINIMIZE == 0时可用。
f_truncate函数截断文件到当前的文件读/写指针。当文件读/写指针已经指向文件结束时，该函数不起作用。