recvfrom - fromlen parameter

i have been fidgeting winsock's udp.

the function recvfrom mainly:

Code:

int recvfrom( SOCKET s, char FAR* buf, int len, int flags, struct sockaddr FAR* from, int FAR* fromlen );

it has been acting strange

when i call:

Code:

char data[6];
int fromlen = sizeof(sockaddr);

int recvfrom( s,  data, sizeof(data), 0, NULL, &fromlen );

i get a WSAEFAULT error.
when i provide NULL instead of &fromlen i get no error.

is this normal? my question is why is it checking from when it is NULL? ( assuming that's the problem )

i would like to hear your thoughts.

Probably because you are passing NULL to the from field. You are basically saying that the from structure you are passing is sizeof(sockaddr). Then you pass NULL for that parameter. You are lying to the function.

in tcp with accept

Code:

SOCKET accept( SOCKET s, struct sockaddr FAR* addr,	int FAR* addrlen );

when i call:

Code:

SOCKET s;
int addrlen = sizeof(sockaddr);

int accept( s, sizeof(data), NULL, &addrlen );

i get a no error.
when i provide NULL instead of &addrlen i get no error.

now i also filled addrlen with sizeof(sockaddr). and the situation looks the same as with the udp recvfrom function where i filled fromlen with sizeof(sockaddr).
that's why i think it's so strange