What is the Difference Between read and recv and Between send and write

Question

What is the difference between read   and recv    and between send   and write   in socket programming in terms of performances  speed and other behaviors

User · Answer

read   and write   are more generic  they work with any file descriptor  However  they won t work on Windows   You can pass additional options to send   and recv    so you may have to used them in some cases

User · Answer

The difference is that recv   send   work only on socket descriptors and let you specify certain options for the actual operation  Those functions are slightly more specialized  for instance  you can set a flag to ignore SIGPIPE  or to send out-of-band messages       Functions read   write   are the universal file descriptor functions working on all descriptors

User · Answer

Per the first hit on Google     read   is equivalent to recv   with a flags parameter of 0  Other values for the flags parameter change the behaviour of recv    Similarly  write   is equivalent to send   with flags    0

User · Answer

Another thing on linux is   send does not allow to operate on non-socket fd  Thus  for example to write on usb port  write is necessary

User · Answer

On Linux I also notice that       Interruption of system calls and library functions by signal handlers   If a signal handler is invoked while a system call or library function call is blocked  then either          the call is automatically restarted after the signal handler returns  or   the call fails with the error EINTR              The details vary across UNIX systems  below  the details for Linux       If  a blocked call to one of the following interfaces is interrupted   by a signal handler  then the call is automatically restarted after          the signal handler returns if the SA RESTART flag was used  otherwise the call fails with the error EINTR          read 2   readv 2   write 2   writev 2   and ioctl 2  calls on  slow  devices                      The  following  interfaces  are  never  restarted after being interrupted by a signal handler  regardless of the use of SA RESTART  they          always fail with the error EINTR when interrupted by a signal handler             Input  socket interfaces  when a timeout   SO RCVTIMEO   has  been  set  on  the  socket  using  setsockopt 2    accept 2    recv 2          recvfrom 2   recvmmsg 2   also with a non-NULL timeout argument   and recvmsg 2      Output   socket  interfaces   when  a  timeout   SO RCVTIMEO   has  been  set on the socket using setsockopt 2   connect 2   send 2          sendto 2   and sendmsg 2        Check man 7 signal for more details     A simple usage would be use signal to avoid recvfrom blocking indefinitely   An example from APUE    include  apue h   include  lt netdb h gt   include  lt errno h gt   include  lt sys socket h gt    define BUFLEN      128  define TIMEOUT     20  void sigalrm int signo       void print uptime int sockfd  struct addrinfo  aip        int     n      char    buf BUFLEN        buf 0    0      if  sendto sockfd  buf  1  0  aip- gt ai addr  aip- gt ai addrlen   lt  0          err sys  sendto error        alarm TIMEOUT         here     if   n   recvfrom sockfd  buf  BUFLEN  0  NULL  NULL    lt  0            if  errno    EINTR              alarm 0           err sys  recv error              alarm 0       write STDOUT FILENO  buf  n      int main int argc  char  argv          struct addrinfo      ailist   aip      struct addrinfo     hint      int                 sockfd  err      struct sigaction    sa       if  argc    2          err quit  usage  ruptime hostname        sa sa handler   sigalrm      sa sa flags   0      sigemptyset  amp sa sa mask       if  sigaction SIGALRM   amp sa  NULL   lt  0          err sys  sigaction error        memset  amp hint  0  sizeof hint        hint ai socktype   SOCK DGRAM      hint ai canonname   NULL      hint ai addr   NULL      hint ai next   NULL      if   err   getaddrinfo argv 1    ruptime    amp hint   amp ailist      0          err quit  getaddrinfo error   s   gai strerror err         for  aip   ailist  aip    NULL  aip   aip- gt ai next            if   sockfd   socket aip- gt ai family  SOCK DGRAM  0    lt  0                err   errno            else               print uptime sockfd  aip               exit 0                        fprintf stderr   can t contact  s   s n   argv 1   strerror err        exit 1

User · Answer

Performance and speed   Aren t those kind of     synonyms  here   Anyway  the recv   call takes flags that read   doesn t  which makes it more powerful  or at least more convenient  That is one difference  I don t think there is a significant performance difference  but haven t tested for it

User · Answer

I just noticed recently that when I used write   on a socket in Windows  it almost works  the FD passed to write   isn t the same as the one passed to send    I used  open osfhandle   to get the FD to pass to write      However  it didn t work when I tried to send binary data that included character 10   write   somewhere inserted character 13 before this   Changing it to send   with a flags parameter of 0 fixed that problem   read   could have the reverse problem if 13-10 are consecutive in the binary data  but I haven t tested it   But that appears to be another possible difference between send   and write

[c] What is the Difference Between read() and recv() , and Between send() and write()?

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