FATFS函数之——f_open & f_read
FATFS函数之——f_open & f_read FATFS函数之——f_open & f_read
刚开始使用f_read和f_write时发现read/write老是出错，仔细查看源码发现，原来f_open文件时需要指定open 方式，
这些个方式影响了后面的文件操作。 刚开始使用f_read和f_write时发现read/write老是出错，仔细查看源码发现，原来f_open文件时需要指定open 方式， 这些个方式影响了后面的文件操作。
f_open函数声明如下： f_open函数声明如下：
FRESULT f_open ( FIL* fp, /* [OUT] Pointer to the file object structure */ const TCHAR* path, /* [IN] File name */ BYTE mode /* [IN] Mode flags */ );参数详细说明如下： FRESULT f_open ( FIL* fp, /* [OUT] Pointer to the file object structure */ const TCHAR* path, /* [IN] File name */ BYTE mode /* [IN] Mode flags */ ); 参数详细说明如下：
fp：Pointer to the blank file object structure to be created.
path： Pointer to a null-terminated string that specifies the file name to open or create.
mode： Mode flags that specifies the type of access and open method for the file. It is specified bya combination of following flags. fp：Pointer to the blank file object structure to be created. path： Pointer to a null-terminated string that specifies the file name to open or create. mode： Mode flags that specifies the type of access and open method for the file. It is specified bya combination of following flags.
path： Pointer to a null-terminated string that specifies the file name to open or create.
mode： Mode flags that specifies the type of access and open method for the file. It is specified bya combination of following flags. fp：Pointer to the blank file object structure to be created. path： Pointer to a null-terminated string that specifies the file name to open or create. mode： Mode flags that specifies the type of access and open method for the file. It is specified bya combination of following flags.
flags如下： flags如下：
刚开始用的组合为FA_READ | FA_WRITE | FA_CREATE_ALWAYS，这样的话就读不出来数据，而换成FA_OPEN_ALWAYS就可以正常的读写了，且看FA_CREATE_ALWAYS最后一句： 刚开始用的组合为FA_READ | FA_WRITE | FA_CREATE_ALWAYS，这样的话就读不出来数据，而换成FA_OPEN_ALWAYS就可以正常的读写了，且看FA_CREATE_ALWAYS最后一句：
it will be truncated and overwritten，意思是如果文件存在，则覆盖，所以会读不出数据。 it will be truncated and overwritten，意思是如果文件存在，则覆盖，所以会读不出数据。
f_read函数声明如下： f_read函数声明如下：
FRESULT f_read ( FIL* fp, /* [IN] File object */ void* buff, /* [OUT] Buffer to store read data */ UINT btr, /* [IN] Number of bytes to read */ UINT* br /* [OUT] Number of bytes read */ );btr是用户要读的数据量，br是实际读取的数据量，这样当判断到br==0时，文件读完。
FRESULT f_read ( FIL* fp, /* [IN] File object */ void* buff, /* [OUT] Buffer to store read data */ UINT btr, /* [IN] Number of bytes to read */ UINT* br /* [OUT] Number of bytes read */ ); btr是用户要读的数据量，br是实际读取的数据量，这样当判断到br==0时，文件读完。