CODEWITHSUNDEEP
delphiarrays
user2075861
user2075861

Reputation: 117

Byte array PAnsiChar in Delphi 2007

I have a byte array with some data...

CommandBytes : array of byte;

And I have a function of a VCL that sends command to a bluetooth printer. The VCL function prototype is this

SendData(PAnsiChar, Cardinal);

"This method transmits bytes from the memory buffer into opened device"

How could I pass correctly the byte array to function to send command to printer?

I'm new to Delphi, I tried:

SendData(PAnsiChar(@CommandBytes[0]), SizeOf(CommandBytes));

but it doesn't work...

Thanks in advance.

Upvotes: 1

Views: 2099

Answers (2)

LU RD
LU RD

Reputation: 34889

The SizeOf(CommandBytes) will return the size of a pointer.

Use Length(CommandBytes) to get the element count in the array, which in this case is the allocated buffer size, since SizeOf(byte) = 1.

Upvotes: 1

David Heffernan
David Heffernan

Reputation: 612794

SizeOf() on a dynamic array yields the size of a pointer. A dynamic array is a reference type that is represented as a pointer to the first element of the array. And hence SizeOf() returns the size of a pointer. And that's no use to you here.

You need to use Length() instead:

SendData(PAnsiChar(@CommandBytes[0]), Length(CommandBytes));

The Length() function returns the number of elements in an array.

What's more, I would probably simplify the way you cast to PAnsiChar. You can do it more concisely like this:

SendData(PAnsiChar(CommandBytes), Length(CommandBytes));

That's meaningful because CommandBytes, being a reference to a dynamic array, points to the first element of the array.

Upvotes: 7

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