Slide 4.14: System calls (cont.)

System Calls (Cont.)

The read_int, read_float, and read_double services read an entire line of input up to and including the newline character. For example, the code below reads an integer value and stores it in RAM location with label int_value (presumably declared in data section), where sw is store word:
```
   li   $v0, 5
   syscall
   sw   $v0, int_value
```
The read_string service has the same semantic implementation as the UNIX library routine fgets.
- It reads up to n-1 characters into a buffer and terminates the string with a null character.
- If fewer than n-1 characters are in the current line, it reads up to and including the newline and terminates the string with a null character.

The malloc service returns the address to a block of memory containing n additional bytes. This would be used for dynamic memory allocation.

The exit service stops a program from running.

String Output	String I/O	Integer Output
.data s1: .ascii "abc" s2: .asciiz "xyz" .text la $a0, s1 li $v0, 4 syscall	.data s: .space 4 .text la $a0, s li $a1, 4 li $v0, 8 syscall # Enter "12345". la $a0, s li $v0, 4 syscall	.data val: .word 0 .text li $v0, 5 syscall # Enter 12345. sw $v0, val la $a0, val li $v0, 1 syscall
Output	Output	Output

String Output

String I/O

Integer Output

       .data
 s1:   .ascii   "abc"
 s2:   .asciiz  "xyz"

       .text
       la  $a0, s1
       li  $v0, 4
       syscall

       .data
 s:    .space   4

       .text 
       la  $a0, s
       li  $a1, 4
       li  $v0, 8
       syscall
 # Enter "12345".
       la  $a0, s
       li  $v0, 4
       syscall

       .data
 val:  .word   0 

       .text 
       li  $v0, 5
       syscall 
       # Enter 12345.
       sw  $v0, val
       la  $a0, val
       li  $v0, 1
       syscall

Output