Question about SdFat O_TRUNC flag for SD.open()

Using Arduino Storage
1 
SD.open("/CHAN_1.dat",  O_TRUNC);

I'm a little confused on what this flag does, and the significance of it. Would greatly appreciate if anyone can explain, thanks.

2

From the SDFat documentation:

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.

What confuses you about this?

3

What does its length shall be truncated to 0 means? Does that mean that all the data is removed if the file already existed before this open call?

4

Yes, that is exactly what it means.

5

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