MIPS：如何在动态内存（堆）中存储字符串

Question

我想编写一个子例程，将字符串作为参数（来自用户输入）并存储在动态内存中。

这是我想出的：

    .data
    name: .space 32 # allocates 32 bytes of memory to store a name

    namePrompt: .asciiz "name: "

    .text
    .globl main

main:

    la $a0, namePrompt
    li $v0, 4 # system call to print a string.
    syscall # print namePrompt.

    la $a0, name # adress where to store the input
    li $a1, 32 # max input size in bytes
    li $v0, 8
    syscall

    la $a0, name # name as first parameter of save_string subroutine
    jal save_string



save_string:

    move $s0, $a0 # s0 = name. 

    # allocate 32 bytes in heap memory.
    li $v0, 9 
    li $a0, 32
    syscall

    sw $s0, 0($v0) # store the name in allocated memory

    jr $ra

但我觉得这不是正确的方法。

另外，之后如何释放 space？

Answer 1

But I have got a feeling this isn't the correct way to do it.

不，您目前只是将字符串的地址存储在堆分配的内存中。如果你想存储它的内容你需要一个循环：

move $s1,$v0
copy:
  lb $t0,($s0)        # Read one byte from the source address
  sb $t0,($s1)        # Store it at the destination address
  addiu $s0,$s0,1
  addiu $s1,$s1,1
  bne $t0,$zero,copy  # Repeat until the NUL terminator has been copied

Also how do I free the space afterwards?

假设模拟器的 sbrk 调用主机 OS 的 sbrk 您可以将负值传递给 sbrk 以缩小程序的堆。

MIPS：如何在动态内存（堆）中存储字符串

MIPS: how to store a string in dynamic memory (heap)

memory-management

mips