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Topic: VirtualWire (Read 3735 times) previous topic - next topic

Vincent19

Hey friend,

I am very confuse and lack of knowledge in using the virtualwire library. Can anyone guide me ?

I dont understand this : vw_send((uint8_t *)msg, strlen(msg));

What is that ? I want to ask, how if I want to just send a number to be received by the receiver ?

For example I want to send a number '2'. So in the receiver code, I can write like if the message received is '2' then blink LED ?

Thanks :D

AWOL

#1
Jan 21, 2013, 04:40 pm Last Edit: Jan 22, 2013, 08:59 pm by AWOL Reason: 1
Code: [Select]
I dont understand this : vw_send((uint8_t *)msg, strlen(msg));
"msg" is a null-terminated C string, probably in a "char" buffer.
So, "strlen" tell you how many characters are in the string (not including the terminator).
"(uint8_t *)" says to the compiler "look, I know I'm not giving you the exact type of pointer (msg) you expect, but it'll be OK. Trust me".
And vw_send sends the buffer.

If you want to send just '2' in this way,
Code: [Select]
vw_send((uint8_t *)"2", 1);
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Vincent19

Still not very clear..is that all about string , data type?

AWOL

There is no string datatype in C - strings are just "char" arrays, with the last position filled with a zero (A true zero, not an ASCII zero).
So, the string "Hello" occupies six consecutive locations in array, 'H', 'e', 'l', 'l', 'o' with '\0', where the backslash signifies to the compiler that is really is zero, not ASCII zero.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Vincent19

So if I use this function vw_send(message, length), the messagee must be an arrary of 8 bits ? And I must include write it like this :
vw_send((uint8_t *)msg, strlen(msg)); ???

What are the alternatives ?

Thanks

PaulS

Quote
the messagee must be an arrary of 8 bits ?

This doesn't make sense. The array can be any number of elements. The size of an element, in bytes, is dependent on the type of the array. All bytes are 8 bits.

Vincent19

If I want to just send number '2',

so can I just write vw_send(2, 1) ?

1 refer to the length of message .

PaulS

Quote
so can I just write vw_send(2, 1) ?

No. For 2 reasons. First '2' is not equal to 2. Second, 2 is an int, not an array, and vw_send only sends arrays.

Vincent19

what do you mean 2 is not equal to 2 ? LOL

So everytime I write vw_send(I must include 'uint8_t', length)  ?

Thanks

PaulS

Quote
what do you mean 2 is not equal to 2 ? LOL

The number 2 and the letter '2' are not equal.

Vincent19

You mean '2' and 'two' ?

PaulS

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You mean '2' and 'two' ?

No, I mean 2 as in 1+1 and the letter '2', between the letter '1' and the letter '3'.

The letter '2' has an ASCII code of 50. So, if you send '2', the value 50 gets sent. If you send 2, the value 2 gets sent.

Vincent19

Ok, I get you. It all about the usage of the ' ' .

So, everytime I sent a message using vw_send, I have to type it like this : vw_send((uint8_t*)msg, length ) ?

PaulS

Quote
So, everytime I sent a message using vw_send, I have to type it like this : vw_send((uint8_t*)msg, length ) ?

Yes.

Vincent19

And I have to define what is msg ?

For example msg = '2' ?

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