從匯編的角度分析C語言

C語言代碼：

[cpp]

1. #include <stdlib.h>
2. #include <stdio.h>
4. void main()
5. {
6. char array1[] = { "123456" };
7. char *pointer1 = "123456";
8. }

匯編代碼：

[html]

1. (gdb) disassemble main
2. Dump of assembler code for function main:
3. 0x08048394 <+0>: push %ebp
4. 0x08048395 <+1>: mov %esp,%ebp
5. 0x08048397 <+3>: sub $0x10,%esp
6. 0x0804839a <+6>: movl $0x34333231,-0xb(%ebp)
7. 0x080483a1 <+13>: movw $0x3635,-0x7(%ebp)
8. 0x080483a7 <+19>: movb $0x0,-0x5(%ebp)
9. 0x080483ab <+23>: movl $0x8048484,-0x4(%ebp)
10. 0x080483b2 <+30>: leave
11. 0x080483b3 <+31>: ret
12. End of assembler dump.
13. (gdb) x/7xb 0x8048484
14. 0x8048484 <__dso_handle+4>: 0x31 0x32 0x33 0x34 0x35 0x36 0x00
15. (gdb)

從<+6><+13><+19>三行可以看出，程序為array1分配了7bytes的內存空間，用來存儲“123456”+‘\0’。

而<+23>行表示將地址0x8048484賦給了pointer1，我們可以查看內存0x8048484之後內容，7bytes正好為“123456”+‘\0’，這裡pointer1只是一個指針，並沒有為其分配內存單元。
那麼下面的這段代碼就不難理解了。

[cpp]

1. #include <stdlib.h>
2. #include <stdio.h>
4. void main()
5. {
6. char array1[] = { "123456" };
7. char array2[] = { "123456" };
8. char *pointer1 = "123456";
9. char *pointer2 = "123456";
10. }

匯編代碼：

[html]

1. (gdb) disassemble main
2. Dump of assembler code for function main:
3. 0x08048394 <+0>: push %ebp
4. 0x08048395 <+1>: mov %esp,%ebp
5. 0x08048397 <+3>: sub $0x20,%esp
6. 0x0804839a <+6>: movl $0x34333231,-0xf(%ebp)
7. 0x080483a1 <+13>: movw $0x3635,-0xb(%ebp)
8. 0x080483a7 <+19>: movb $0x0,-0x9(%ebp)
9. 0x080483ab <+23>: movl $0x34333231,-0x16(%ebp)
10. 0x080483b2 <+30>: movw $0x3635,-0x12(%ebp)
11. 0x080483b8 <+36>: movb $0x0,-0x10(%ebp)
12. 0x080483bc <+40>: movl $0x8048494,-0x4(%ebp)
13. 0x080483c3 <+47>: movl $0x8048494,-0x8(%ebp)
14. 0x080483ca <+54>: leave
15. 0x080483cb <+55>: ret
16. End of assembler dump.
17. (gdb) x/7xb 0x8048494
18. 0x8048494 <__dso_handle+4>: 0x31 0x32 0x33 0x34 0x35 0x36 0x00
19. (gdb)

接著這段代碼也就順其自然了！ [html]

1. (gdb) disassemble main
2. Dump of assembler code for function main:
3. 0x08048394 <+0>: push %ebp
4. 0x08048395 <+1>: mov %esp,%ebp
5. 0x08048397 <+3>: sub $0x20,%esp
6. 0x0804839a <+6>: movl $0x34333231,-0xf(%ebp)
7. 0x080483a1 <+13>: movw $0x3635,-0xb(%ebp)
8. 0x080483a7 <+19>: movb $0x0,-0x9(%ebp)
9. 0x080483ab <+23>: movl $0x34333231,-0x16(%ebp)
10. 0x080483b2 <+30>: movw $0x3635,-0x12(%ebp)
11. 0x080483b8 <+36>: movb $0x0,-0x10(%ebp)
12. 0x080483bc <+40>: movl $0x8048494,-0x4(%ebp)
13. 0x080483c3 <+47>: movl $0x804849b,-0x8(%ebp)
14. 0x080483ca <+54>: leave
15. 0x080483cb <+55>: ret
16. End of assembler dump.
17. (gdb) x/7xb 0x8048494
18. 0x8048494 <__dso_handle+4>: 0x31 0x32 0x33 0x34 0x35 0x36 0x00
19. (gdb) x/9xb 0x804849b
20. 0x804849b <__dso_handle+11>: 0x31 0x32 0x33 0x34 0x35 0x36 0x37 0x38
21. 0x80484a3 <__dso_handle+19>: 0x00
22. (gdb)