I have read that its possible to replace
but not insert.
So the question is:is there a way to rewrite everything on line 3.
print() writes at the end of the file? right?
aFile = SD.open("data.txt", FILE_READ);
In what other ways are FILE_READ and FILE_WRITE different than the fact that you can actually use print in FILE_WRITE mode?
guess that the above might be faster? or else why do you have it at all?
NOTE: saw that FILE_WRITE starts at the end of the file too.
i should be able to use aFile.seek(0); to move to the front? right?
You are talking about "append mode" and "truncate mode", never herd of those and never came across any examples with those within, care to explain how I could use this modes to my advantage?
#define FILE_READ O_READ#define FILE_WRITE (O_READ | O_WRITE | O_CREAT)
/** * Open a file or directory by name. * * \param[in] dirFile An open SdFat instance for the directory containing the * file to be opened. * * \param[in] fileName A valid 8.3 DOS name for a file to be opened. * * \param[in] oflag Values for \a oflag are constructed by a bitwise-inclusive * OR of flags from the following list * * O_READ - Open for reading. * * O_RDONLY - Same as O_READ. * * O_WRITE - Open for writing. * * O_WRONLY - Same as O_WRITE. * * O_RDWR - Open for reading and writing. * * O_APPEND - If set, the file offset shall be set to the end of the * file prior to each write. * * O_CREAT - If the file exists, this flag has no effect except as noted * under O_EXCL below. Otherwise, the file shall be created * * O_EXCL - If O_CREAT and O_EXCL are set, open() shall fail if the file exists. * * O_SYNC - Call sync() after each write. This flag should not be used with * write(uint8_t), write_P(PGM_P), writeln_P(PGM_P), or the Arduino Print class. * These functions do character at a time writes so sync() will be called * after each byte. * * O_TRUNC - If the file exists and is a regular file, and the file is * successfully opened and is not read only, its length shall be truncated to 0. * * \note Directory files must be opened read only. Write and truncation is * not allowed for directory files. * * \return The value one, true, is returned for success and * the value zero, false, is returned for failure. * Reasons for failure include this SdFile is already open, \a difFile is not * a directory, \a fileName is invalid, the file does not exist * or can't be opened in the access mode specified by oflag. */
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