What is the proper way to read a number (int) from a binary file?

[elgs]

I want to:

1. seek to position p from the beginning of a binary file;
2. read the next 4 bytes;
3. and turn what's read into a number (32bit integer);

I can do the first with Deno.seek, but Deno.read doesn't provide a parameter for how many bytes to read. So how can I do it? Thanks.

[caspervonb]

but Deno.read doesn't provide a parameter for how many bytes to read.

It does, it can only read up to N bytes where the number of bytes is the byteLength of the TypedArray passed in.

• Seek to the offset,
• Pass an Uint8Array with a byteLength of 4 to Deno.read
• Use a DataView and call getInt32(0) to read that back as i32 (getUint32 for u32).

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[elgs]

Thank you so much!

[kbridge]

You can use readRange from std/io/files.ts. (Documentation) It encapsulates the seeking to the offset and reading N bytes to a Uint8Array steps. (Source Code) It's the same as the first two steps of @caspervonb's answer, so it's equivalent but saves some boilerplate code.