FATFS 初学之 f_truncate

/*-----------------------------------------------------------------------*/
/* Truncate File                                                         */
/*-----------------------------------------------------------------------*/

FRESULT f_truncate (
    FIL *fp        /* Pointer to the file object */
)
{
    FRESULT res;
    DWORD ncl;


    res = validate(fp->fs, fp->id);        /* Check validity of the object */
    if (res == FR_OK) {
        if (fp->flag & FA__ERROR) {            /* Check abort flag */
            res = FR_INT_ERR;
        } else {
            if (!(fp->flag & FA_WRITE))        /* Check access mode */
                res = FR_DENIED;
        }
    }
    if (res == FR_OK) {
        if (fp->fsize > fp->fptr) {
            fp->fsize = fp->fptr;    /* Set file size to current R/W point */
            fp->flag |= FA__WRITTEN;
            if (fp->fptr == 0) {    /* When set file size to zero, remove entire cluster chain */
                res = remove_chain(fp->fs, fp->sclust);
                fp->sclust = 0;
            } else {                /* When truncate a part of the file, remove remaining clusters */
                ncl = get_fat(fp->fs, fp->clust);
                res = FR_OK;
                if (ncl == 0xFFFFFFFF) res = FR_DISK_ERR;
                if (ncl == 1) res = FR_INT_ERR;
                if (res == FR_OK && ncl < fp->fs->n_fatent) {
                    res = put_fat(fp->fs, fp->clust, 0x0FFFFFFF);
                    if (res == FR_OK) res = remove_chain(fp->fs, ncl);
                }
            }
        }
        if (res != FR_OK) fp->flag |= FA__ERROR;
    }

    LEAVE_FF(fp->fs, res);
}

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。