Read String

The trap handler can also read in a string from the keyboard.

li      $v0,8       # code 8 == read string
lw      $a0,buffer  # $a0 == address of buffer
li      $a1,16      # $a1 == buffer length
syscall             # Invoke the operating system.

 . . . .

        .data
buffer: .space 16   # reserve 16 bytes

Details: Usually $a1 contains the length (in bytes) of the input buffer. Up to ($a1)-1 characters are read from the keyboard and placed in buffer as a null terminated string. The last byte of the buffer is filled with null.

The user ends the string by hitting "enter". The "enter" character appears in the buffer as the byte '\n', 0x0a. This byte is followed by the null byte 0x00. If the user enters a string that is exactly ($a1)-1 characters long the "enter" character is omitted from the buffer. No matter what, there is a null at the end of data in the buffer.