CODEWITHSUNDEEP
clinuxsocketssend
user1386966
user1386966

Reputation: 3392

sending data using send() function in linux

I read the documentation regarding send() function, when it was said that the third parameter (len) is "The length, in bytes, of the data in buffer pointed to by the buf parameter".

I can't seem to understand if it sends the number of bytes I pass, or I nedd to pass the size of the buffer and it sends all the data included there.

Exmaple:

#define X 256

// main :
char test[X] = {0};
memcpy(test, "hello", 6);
send(sockfd, test, 6, 0)
send(sockfd, test, 256,0)
// will the first opetion send only hello? or hello000000....?

Thanks!

Upvotes: 0

Views: 2131

Answers (2)

Jite
Jite

Reputation: 4368

As a complement to David Schwartz proper answer:

Depending on if the socket is non-blocking,or not, it is NOT guaranteed that a single send will actually send all data. You must check return value and might have to call send again (with correct buffer offsets).

For instance if you want to send 10 bytes of data (len=10), you call send(sock, buf, len, 0). However lets say it only manages to send 5 bytes, then send(..) will return 5, meaning that you will have to call it again later like send(sock, (buf + 5), (len - 5), 0). Meaning, skip first five bytes in buffer, they're already sent, and withdraw five bytes from the total number of bytes (len) we want to send.

(Note that I used parenthesis to make it easier to read only, and it assumes that buf is a pointer to 1 byte type.)

Upvotes: 2

David Schwartz
David Schwartz

Reputation: 182743

The send function sends precisely the number of bytes you tell it to (assuming it's not interrupted and doesn't otherwise fail). The number of bytes you need to send is determined by the protocol you are implementing. For example, if the protocol says you should send "FOO\r\n", then you need to send 5 bytes. If the protocol specifies that integers are represented as 4 bytes in network byte order and you're sending an integer, the buffer should contain an integer in network byte order and you should send 4 bytes. The size of the buffer doesn't matter to send.

Upvotes: 2

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