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Jiho Kang
Jiho Kang

Reputation: 2492

Will writeToFile:atomically: overwrite data?

Really simple question but it doesn't seem to be clear in Apple's docs.

Will writeToFile:atomically: for NSData, NSArray etc. overwrite existing data on a file?

Upvotes: 97

Views: 18778

Answers (2)

BJ Homer
BJ Homer

Reputation: 49034

Yes. writeToFile:atomically: will.

Upvotes: 223

Igor
Igor

Reputation: 12303

Method writeToFile:atomically: ALWAYS OVERWRITE FILE, regardless of the atomically: YES or NO.

Information from Apple docs (NSData, section "Saving Data"):

The NSData class and its subclasses provide methods to quickly and easily save their contents to disk. To minimize the risk of data loss, these methods provide the option of saving the data atomically. Atomic writes guarantee that the data is either saved in its entirety, or it fails completely. The atomic write begins by writing the data to a temporary file. If this write succeeds, then the method moves the temporary file to its final location.

No one word about checking if file exist.

For example, for method copyItemAtPath:toPath:error: in docs (NSFileManager, section Discussion) specifically written about such checking:

If a file with the same name already exists at dstPath, this method stops the copy attempt and returns an appropriate error.

Upvotes: 7

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