[已解决]问一下拷贝字符串，问一下为什么可以正常打印而且值是一样的

摸你穷

#include <stdio.h>
#include<string.h>

int main()
{
        char str1[]= "Original string";
        char str2[]="string";

        strcpy(str2,str1);

        printf("%s\n",str2);
        printf("%s\n",str1);

        return 0;
}

最佳答案

月排行榜 / 总排行榜

人造人

2022-1-29 22:44:16

摸你穷 发表于 2022-1-29 22:58
为了避免溢出，必须确保用于存放的数组长度足以容纳待拷贝的字符串（注意：长度需要包含结束符 '\0'）。
...

这个代码不是所有机器上都能运行
这代码行为是未定义的，不同的机器很可能会给出不同的结果

调试环境直接报错

1. $ cat main.c
   
2. #include <stdio.h>
   
3. #include<string.h>
   
4. 
   
5. int main()
   
6. {
   
7.         char str1[]= "Original string";
   
8.         char str2[]="string";
   
9. 
   
10.         strcpy(str2,str1);
    
11. 
    
12.         printf("%s\n",str2);
    
13.         printf("%s\n",str1);
    
14. 
    
15.         return 0;
    
16. }
    
17. $ gcc-debug -o main main.c
    
18. $ ./main
    
19. =================================================================
    
20. ==3378990==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffd921cbd07 at pc 0x7f736c753c1b bp 0x7ffd921cbcd0 sp 0x7ffd921cb478
    
21. WRITE of size 16 at 0x7ffd921cbd07 thread T0
    
22.     #0 0x7f736c753c1a in __interceptor_strcpy /build/gcc/src/gcc/libsanitizer/asan/asan_interceptors.cpp:440
    
23.     #1 0x5625bd5a832c in main /tmp/main.c:9
    
24.     #2 0x7f736bbe8b24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
    
25.     #3 0x5625bd5a80fd in _start (/tmp/main+0x10fd)
    
26. 
    
27. Address 0x7ffd921cbd07 is located in stack of thread T0 at offset 39 in frame
    
28.     #0 0x5625bd5a81d8 in main /tmp/main.c:5
    
29. 
    
30.   This frame has 2 object(s):
    
31.     [32, 39) 'str2' (line 7) <== Memory access at offset 39 overflows this variable
    
32.     [64, 80) 'str1' (line 6)
    
33. HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
    
34.       (longjmp and C++ exceptions *are* supported)
    
35. SUMMARY: AddressSanitizer: stack-buffer-overflow /build/gcc/src/gcc/libsanitizer/asan/asan_interceptors.cpp:440 in __interceptor_strcpy
    
36. Shadow bytes around the buggy address:
    
37.   0x100032431750: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
38.   0x100032431760: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
39.   0x100032431770: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
40.   0x100032431780: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
41.   0x100032431790: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
    
42. =>0x1000324317a0:[07]f2 f2 f2 00 00 f3 f3 00 00 00 00 00 00 00 00
    
43.   0x1000324317b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
44.   0x1000324317c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
45.   0x1000324317d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
46.   0x1000324317e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
47.   0x1000324317f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
48. Shadow byte legend (one shadow byte represents 8 application bytes):
    
49.   Addressable:           00
    
50.   Partially addressable: 01 02 03 04 05 06 07
    
51.   Heap left redzone:       fa
    
52.   Freed heap region:       fd
    
53.   Stack left redzone:      f1
    
54.   Stack mid redzone:       f2
    
55.   Stack right redzone:     f3
    
56.   Stack after return:      f5
    
57.   Stack use after scope:   f8
    
58.   Global redzone:          f9
    
59.   Global init order:       f6
    
60.   Poisoned by user:        f7
    
61.   Container overflow:      fc
    
62.   Array cookie:            ac
    
63.   Intra object redzone:    bb
    
64.   ASan internal:           fe
    
65.   Left alloca redzone:     ca
    
66.   Right alloca redzone:    cb
    
67.   Shadow gap:              cc
    
68. ==3378990==ABORTING
    
69. $

复制代码

1. $ clang -o main main.c
   
2. $ ./main
   
3. Original string
   
4. string
   
5. $ gcc -o main main.c
   
6. $ ./main
   
7. Original string
   
8. l string
   
9. $

复制代码

跳转到最佳答案楼层

人造人

摸你穷 发表于 2022-1-29 22:58
为了避免溢出，必须确保用于存放的数组长度足以容纳待拷贝的字符串（注意：长度需要包含结束符 '\0'）。
...

这个代码不是所有机器上都能运行
这代码行为是未定义的，不同的机器很可能会给出不同的结果

调试环境直接报错

1. $ cat main.c
   
2. #include <stdio.h>
   
3. #include<string.h>
   
4. 
   
5. int main()
   
6. {
   
7.         char str1[]= "Original string";
   
8.         char str2[]="string";
   
9. 
   
10.         strcpy(str2,str1);
    
11. 
    
12.         printf("%s\n",str2);
    
13.         printf("%s\n",str1);
    
14. 
    
15.         return 0;
    
16. }
    
17. $ gcc-debug -o main main.c
    
18. $ ./main
    
19. =================================================================
    
20. ==3378990==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffd921cbd07 at pc 0x7f736c753c1b bp 0x7ffd921cbcd0 sp 0x7ffd921cb478
    
21. WRITE of size 16 at 0x7ffd921cbd07 thread T0
    
22.     #0 0x7f736c753c1a in __interceptor_strcpy /build/gcc/src/gcc/libsanitizer/asan/asan_interceptors.cpp:440
    
23.     #1 0x5625bd5a832c in main /tmp/main.c:9
    
24.     #2 0x7f736bbe8b24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
    
25.     #3 0x5625bd5a80fd in _start (/tmp/main+0x10fd)
    
26. 
    
27. Address 0x7ffd921cbd07 is located in stack of thread T0 at offset 39 in frame
    
28.     #0 0x5625bd5a81d8 in main /tmp/main.c:5
    
29. 
    
30.   This frame has 2 object(s):
    
31.     [32, 39) 'str2' (line 7) <== Memory access at offset 39 overflows this variable
    
32.     [64, 80) 'str1' (line 6)
    
33. HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
    
34.       (longjmp and C++ exceptions *are* supported)
    
35. SUMMARY: AddressSanitizer: stack-buffer-overflow /build/gcc/src/gcc/libsanitizer/asan/asan_interceptors.cpp:440 in __interceptor_strcpy
    
36. Shadow bytes around the buggy address:
    
37.   0x100032431750: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
38.   0x100032431760: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
39.   0x100032431770: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
40.   0x100032431780: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
41.   0x100032431790: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
    
42. =>0x1000324317a0:[07]f2 f2 f2 00 00 f3 f3 00 00 00 00 00 00 00 00
    
43.   0x1000324317b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
44.   0x1000324317c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
45.   0x1000324317d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
46.   0x1000324317e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
47.   0x1000324317f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
48. Shadow byte legend (one shadow byte represents 8 application bytes):
    
49.   Addressable:           00
    
50.   Partially addressable: 01 02 03 04 05 06 07
    
51.   Heap left redzone:       fa
    
52.   Freed heap region:       fd
    
53.   Stack left redzone:      f1
    
54.   Stack mid redzone:       f2
    
55.   Stack right redzone:     f3
    
56.   Stack after return:      f5
    
57.   Stack use after scope:   f8
    
58.   Global redzone:          f9
    
59.   Global init order:       f6
    
60.   Poisoned by user:        f7
    
61.   Container overflow:      fc
    
62.   Array cookie:            ac
    
63.   Intra object redzone:    bb
    
64.   ASan internal:           fe
    
65.   Left alloca redzone:     ca
    
66.   Right alloca redzone:    cb
    
67.   Shadow gap:              cc
    
68. ==3378990==ABORTING
    
69. $

复制代码

1. $ clang -o main main.c
   
2. $ ./main
   
3. Original string
   
4. string
   
5. $ gcc -o main main.c
   
6. $ ./main
   
7. Original string
   
8. l string
   
9. $

复制代码

weekend2000

str1 拷贝给 str2，str1 的值覆盖了 str2 原有的值，所以是一样的啊

摸你穷

weekend2000 发表于 2022-1-29 22:47
str1 拷贝给 str2，str1 的值覆盖了 str2 原有的值，所以是一样的啊

可是两个字节不一样为什么可以正常拷贝并打印了

weekend2000

这个是strcyp()函数的功能，如果有兴趣的话可以去看一看strcpy()函数的源码。

摸你穷

weekend2000 发表于 2022-1-29 22:50
这个是strcyp()函数的功能，如果有兴趣的话可以去看一看strcpy()函数的源码。

为了避免溢出，必须确保用于存放的数组长度足以容纳待拷贝的字符串（注意：长度需要包含结束符 '\0'）。
这是原话，可是对啊这里str1（16个字节）拷贝到str2（7个字节）明显是装不下啊，最重要的是最后打印str1和str2都是Original string

weekend2000

人造人 发表于 2022-1-29 22:44
这个代码不是所有机器上都能运行
这代码行为是未定义的，不同的机器很可能会给出不同的结果

是因为strcpy没有边界检查，所以不同规格编译器运行结果也不同吗

人造人

weekend2000 发表于 2022-2-1 08:12
是因为strcpy没有边界检查，所以不同规格编译器运行结果也不同吗

也可以这么理解