Reading from stdin

Question

What are the possible ways for reading user input using read   system call in Unix  How can we read from stdin byte by byte using read

User · Answer

You can do something like this to read 10 bytes:

char buffer[10];
read(STDIN_FILENO, buffer, 10);

remember read() doesn't add '\0' to terminate to make it string (just gives raw buffer).

To read 1 byte at a time:

char ch;
while(read(STDIN_FILENO, &ch, 1) > 0)
{
 //do stuff
}

and don't forget to #include <unistd.h>, STDIN_FILENO defined as macro in this file.

There are three standard POSIX file descriptors, corresponding to the three standard streams, which presumably every process should expect to have:

Integer value   Name
       0        Standard input (stdin)
       1        Standard output (stdout)
       2        Standard error (stderr)

So instead STDIN_FILENO you can use 0.

Edit:
In Linux System you can find this using following command:

$ sudo grep 'STDIN_FILENO' /usr/include/* -R | grep 'define'
/usr/include/unistd.h:#define   STDIN_FILENO    0   /* Standard input.  */

Notice the comment /* Standard input. */

User · Answer

From the man read    include  lt unistd h gt  ssize t read int fd  void  buf  size t count     Input parameters    int fd file descriptor is an integer and not a file pointer  The file descriptor for stdin is 0 void  buf pointer to buffer to store characters read by the read function size t count maximum number of characters to read   So you can read character by character with the following code   char buf 1    while read 0  buf  sizeof buf   gt 0          read   here read from stdin charachter by character       the buf 0  contains the character got by read

[c] Reading from stdin

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