c 语言 scanf函数的使用

人造人

傻眼貓咪 发表于 2022-3-6 12:31
哇
可以知道用的是什么编译器吗？我想找这种超级敏感，报错多多的编译器学习学习

其实gcc就自带了内存检查的功能(运行时检查)，只是默认没有开启
当然，要你的gcc是新版本的，旧版本的gcc有可能用不了
我不知道gcc从哪一个版本开始添加的内存检查功能，也不关心
反正我的gcc是新版本的，可以用内存检查，^_^

1. $ gcc --version
   
2. gcc (GCC) 11.2.0
   
3. Copyright (C) 2021 Free Software Foundation, Inc.
   
4. This is free software; see the source for copying conditions.  There is NO
   
5. warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   
6. 
   
7. $

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谈不上最新，但是够用
我没有在windows中尝试过gcc的内存检查功能，可能也能用？不知道

1. $ cat main.c
   
2. #include <stdio.h>
   
3. #include <stdlib.h>
   
4. 
   
5. int main(void) {
   
6.     int *p = malloc(sizeof(*p));
   
7.     *p = 123;
   
8.     printf("%d\n", *p);
   
9.     //free(p);
   
10.     return 0;
    
11. }
    
12. $ gcc -g -Wall -fsanitize=undefined -fsanitize=leak -fsanitize=address -fno-omit-frame-pointer -o main main.c
    
13. $ ./main
    
14. 123
    
15. 
    
16. =================================================================
    
17. ==987243==ERROR: LeakSanitizer: detected memory leaks
    
18. 
    
19. Direct leak of 4 byte(s) in 1 object(s) allocated from:
    
20.     #0 0x7ff146f8cdd9 in __interceptor_malloc /usr/src/debug/gcc/libsanitizer/asan/asan_malloc_linux.cpp:145
    
21.     #1 0x560d4f9611ba in main /tmp/C/main.c:5
    
22.     #2 0x7ff14638330f in __libc_start_call_main (/usr/lib/libc.so.6+0x2d30f)
    
23. 
    
24. SUMMARY: AddressSanitizer: 4 byte(s) leaked in 1 allocation(s).
    
25. $ vim main.c
    
26. $ cat main.c
    
27. #include <stdio.h>
    
28. #include <stdlib.h>
    
29. 
    
30. int main(void) {
    
31.     int *p = malloc(sizeof(*p));
    
32.     *p = 123;
    
33.     printf("%d\n", *p);
    
34.     free(p);
    
35.     return 0;
    
36. }
    
37. $ gcc -g -Wall -fsanitize=undefined -fsanitize=leak -fsanitize=address -fno-omit-frame-pointer -o main main.c
    
38. $ ./main
    
39. 123
    
40. $
    

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1. $ cat main.c
   
2. #include <stdio.h>
   
3. #include <stdlib.h>
   
4. 
   
5. int main(void) {
   
6.     int array[10] = {0};
   
7.     int n;
   
8.     scanf("%d", &n);
   
9.     printf("%d\n", array[n]);
   
10.     return 0;
    
11. }
    
12. $ gcc -g -Wall -fsanitize=undefined -fsanitize=leak -fsanitize=address -fno-omit-frame-pointer -o main main.c
    
13. $ ./main
    
14. 10
    
15. main.c:8:25: runtime error: index 10 out of bounds for type 'int [10]'
    
16. main.c:8:5: runtime error: load of address 0x7ffdd3b78528 with insufficient space for an object of type 'int'
    
17. 0x7ffdd3b78528: note: pointer points here
    
18. 00 00 00 00  00 a6 3c 78 98 8a 28 12  c0 84 b7 d3 fd 7f 00 00  c0 7a fa 5c bf 7f 00 00  41 00 00 00
    
19.               ^
    
20. =================================================================
    
21. ==988335==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffdd3b78528 at pc 0x55c36c0db465 bp 0x7ffdd3b784c0 sp 0x7ffdd3b784b0
    
22. READ of size 4 at 0x7ffdd3b78528 thread T0
    
23.     #0 0x55c36c0db464 in main /tmp/C/main.c:8
    
24.     #1 0x7fbf5ba2030f in __libc_start_call_main (/usr/lib/libc.so.6+0x2d30f)
    
25.     #2 0x7fbf5ba203c0 in __libc_start_main@GLIBC_2.2.5 (/usr/lib/libc.so.6+0x2d3c0)
    
26.     #3 0x55c36c0db124 in _start (/tmp/C/main+0x1124)
    
27. 
    
28. Address 0x7ffdd3b78528 is located in stack of thread T0 at offset 88 in frame
    
29.     #0 0x55c36c0db208 in main /tmp/C/main.c:4
    
30. 
    
31.   This frame has 2 object(s):
    
32.     [32, 36) 'n' (line 6)
    
33.     [48, 88) 'array' (line 5) <== Memory access at offset 88 overflows this variable
    
34. HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
    
35.       (longjmp and C++ exceptions *are* supported)
    
36. SUMMARY: AddressSanitizer: stack-buffer-overflow /tmp/C/main.c:8 in main
    
37. Shadow bytes around the buggy address:
    
38.   0x10003a767050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
39.   0x10003a767060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
40.   0x10003a767070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
41.   0x10003a767080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
42.   0x10003a767090: 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 04 f2
    
43. =>0x10003a7670a0: 00 00 00 00 00[f3]f3 f3 f3 f3 00 00 00 00 00 00
    
44.   0x10003a7670b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
45.   0x10003a7670c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
46.   0x10003a7670d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
47.   0x10003a7670e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
48.   0x10003a7670f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
49. Shadow byte legend (one shadow byte represents 8 application bytes):
    
50.   Addressable:           00
    
51.   Partially addressable: 01 02 03 04 05 06 07
    
52.   Heap left redzone:       fa
    
53.   Freed heap region:       fd
    
54.   Stack left redzone:      f1
    
55.   Stack mid redzone:       f2
    
56.   Stack right redzone:     f3
    
57.   Stack after return:      f5
    
58.   Stack use after scope:   f8
    
59.   Global redzone:          f9
    
60.   Global init order:       f6
    
61.   Poisoned by user:        f7
    
62.   Container overflow:      fc
    
63.   Array cookie:            ac
    
64.   Intra object redzone:    bb
    
65.   ASan internal:           fe
    
66.   Left alloca redzone:     ca
    
67.   Right alloca redzone:    cb
    
68.   Shadow gap:              cc
    
69. ==988335==ABORTING
    
70. $
    
71. $
    
72. $
    
73. $
    
74. $
    
75. $
    
76. $ vim main.c
    
77. $ cat main.c
    
78. #include <stdio.h>
    
79. #include <stdlib.h>
    
80. 
    
81. int main(void) {
    
82.     int array[10] = {0};
    
83.     int n;
    
84.     scanf("%d", &n);
    
85.     array[n] = 123;
    
86.     //printf("%d\n", array[n]);
    
87.     return 0;
    
88. }
    
89. $ gcc -g -Wall -fsanitize=undefined -fsanitize=leak -fsanitize=address -fno-omit-frame-pointer -o main main.c
    
90. main.c: In function ‘main’:
    
91. main.c:5:9: warning: variable ‘array’ set but not used [-Wunused-but-set-variable]
    
92.     5 |     int array[10] = {0};
    
93.       |         ^~~~~
    
94. $ ./main
    
95. 10
    
96. main.c:8:10: runtime error: index 10 out of bounds for type 'int [10]'
    
97. main.c:8:14: runtime error: store to address 0x7ffec538b1b8 with insufficient space for an object of type 'int'
    
98. 0x7ffec538b1b8: note: pointer points here
    
99. 00 00 00 00  00 66 e4 ec 51 d5 04 37  50 b1 38 c5 fe 7f 00 00  c0 4a 7a 7c eb 7f 00 00  41 00 00 00
    
100.               ^
     
101. =================================================================
     
102. ==988793==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffec538b1b8 at pc 0x55d75b226465 bp 0x7ffec538b150 sp 0x7ffec538b140
     
103. WRITE of size 4 at 0x7ffec538b1b8 thread T0
     
104.     #0 0x55d75b226464 in main /tmp/C/main.c:8
     
105.     #1 0x7feb7b21d30f in __libc_start_call_main (/usr/lib/libc.so.6+0x2d30f)
     
106.     #2 0x7feb7b21d3c0 in __libc_start_main@GLIBC_2.2.5 (/usr/lib/libc.so.6+0x2d3c0)
     
107.     #3 0x55d75b226124 in _start (/tmp/C/main+0x1124)
     
108. 
     
109. Address 0x7ffec538b1b8 is located in stack of thread T0 at offset 88 in frame
     
110.     #0 0x55d75b226208 in main /tmp/C/main.c:4
     
111. 
     
112.   This frame has 2 object(s):
     
113.     [32, 36) 'n' (line 6)
     
114.     [48, 88) 'array' (line 5) <== Memory access at offset 88 overflows this variable
     
115. HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
     
116.       (longjmp and C++ exceptions *are* supported)
     
117. SUMMARY: AddressSanitizer: stack-buffer-overflow /tmp/C/main.c:8 in main
     
118. Shadow bytes around the buggy address:
     
119.   0x100058a695e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     
120.   0x100058a695f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     
121.   0x100058a69600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     
122.   0x100058a69610: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     
123.   0x100058a69620: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
     
124. =>0x100058a69630: 04 f2 00 00 00 00 00[f3]f3 f3 f3 f3 00 00 00 00
     
125.   0x100058a69640: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     
126.   0x100058a69650: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     
127.   0x100058a69660: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     
128.   0x100058a69670: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     
129.   0x100058a69680: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     
130. Shadow byte legend (one shadow byte represents 8 application bytes):
     
131.   Addressable:           00
     
132.   Partially addressable: 01 02 03 04 05 06 07
     
133.   Heap left redzone:       fa
     
134.   Freed heap region:       fd
     
135.   Stack left redzone:      f1
     
136.   Stack mid redzone:       f2
     
137.   Stack right redzone:     f3
     
138.   Stack after return:      f5
     
139.   Stack use after scope:   f8
     
140.   Global redzone:          f9
     
141.   Global init order:       f6
     
142.   Poisoned by user:        f7
     
143.   Container overflow:      fc
     
144.   Array cookie:            ac
     
145.   Intra object redzone:    bb
     
146.   ASan internal:           fe
     
147.   Left alloca redzone:     ca
     
148.   Right alloca redzone:    cb
     
149.   Shadow gap:              cc
     
150. ==988793==ABORTING
     
151. $
     

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你可能会发现，我有时候用的编译命令是这样的

1. gcc-debug -o main main.c

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这个 gcc-debug 其实是一个 alias

1. alias gcc-debug='gcc -g -Wall -fsanitize=undefined -fsanitize=leak -fsanitize=address -fno-omit-frame-pointer'
   

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其实下面这两个是一样的

1. gcc-debug -o main main.c

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1. $ gcc -g -Wall -fsanitize=undefined -fsanitize=leak -fsanitize=address -fno-omit-frame-pointer -o main main.c

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我为了避免每一次编译代码都输入那么一长串，就弄了一个alias

这个报错的内容可以说是很详细了，代码的哪一行，变量的值，堆栈的当前状态
这些都给你列出来了，对debug非常有帮助
大部分的逻辑问题（逻辑错误），gcc的运行时检查都能检查出来
大部分的语法问题（语法错误），gcc的-Wall选项也全都给你指出来了
所以，写的代码很难出问题吧？
还有，其实我这边的报错是彩色的，看起来更舒服，^_^

人造人

1. $ alias gcc-debug
   
2. alias gcc-debug='gcc -g -Wall -fsanitize=undefined -fsanitize=leak -fsanitize=address -fno-omit-frame-pointer'
   
3. $ cat main.c
   
4. #include <stdio.h>
   
5. #include <stdlib.h>
   
6. 
   
7. int main(void) {
   
8.     int array[10] = {0};
   
9.     int n;
   
10.     scanf("%d", &n);
    
11.     array[n] = 123;
    
12.     //printf("%d\n", array[n]);
    
13.     return 0;
    
14. }
    
15. $ ls
    
16. main  main.c
    
17. $ rm main
    
18. $ ls
    
19. main.c
    
20. $ gcc-debug -o main main.c
    
21. main.c: In function ‘main’:
    
22. main.c:5:9: warning: variable ‘array’ set but not used [-Wunused-but-set-variable]
    
23.     5 |     int array[10] = {0};
    
24.       |         ^~~~~
    
25. $ ./main
    
26. 13
    
27. main.c:8:10: runtime error: index 13 out of bounds for type 'int [10]'
    
28. main.c:8:14: runtime error: store to address 0x7ffcc7b9b984 with insufficient space for an object of type 'int'
    
29. 0x7ffcc7b9b984: note: pointer points here
    
30.   10 b9 b9 c7 fc 7f 00 00  c0 5a 67 e2 00 7f 00 00  41 00 00 00 60 60 00 00  3c e1 27 e1 00 7f 00 00
    
31.               ^
    
32. =================================================================
    
33. ==989484==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffcc7b9b984 at pc 0x559bea5db465 bp 0x7ffcc7b9b910 sp 0x7ffcc7b9b900
    
34. WRITE of size 4 at 0x7ffcc7b9b984 thread T0
    
35.     #0 0x559bea5db464 in main /tmp/C/main.c:8
    
36.     #1 0x7f00e10ee30f in __libc_start_call_main (/usr/lib/libc.so.6+0x2d30f)
    
37.     #2 0x7f00e10ee3c0 in __libc_start_main@GLIBC_2.2.5 (/usr/lib/libc.so.6+0x2d3c0)
    
38.     #3 0x559bea5db124 in _start (/tmp/C/main+0x1124)
    
39. 
    
40. Address 0x7ffcc7b9b984 is located in stack of thread T0 at offset 100 in frame
    
41.     #0 0x559bea5db208 in main /tmp/C/main.c:4
    
42. 
    
43.   This frame has 2 object(s):
    
44.     [32, 36) 'n' (line 6)
    
45.     [48, 88) 'array' (line 5) <== Memory access at offset 100 overflows this variable
    
46. HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
    
47.       (longjmp and C++ exceptions *are* supported)
    
48. SUMMARY: AddressSanitizer: stack-buffer-overflow /tmp/C/main.c:8 in main
    
49. Shadow bytes around the buggy address:
    
50.   0x100018f6b6e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
51.   0x100018f6b6f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
52.   0x100018f6b700: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
53.   0x100018f6b710: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
54.   0x100018f6b720: 00 00 00 00 f1 f1 f1 f1 04 f2 00 00 00 00 00 f3
    
55. =>0x100018f6b730:[f3]f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
    
56.   0x100018f6b740: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
57.   0x100018f6b750: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
58.   0x100018f6b760: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
59.   0x100018f6b770: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
60.   0x100018f6b780: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    
61. Shadow byte legend (one shadow byte represents 8 application bytes):
    
62.   Addressable:           00
    
63.   Partially addressable: 01 02 03 04 05 06 07
    
64.   Heap left redzone:       fa
    
65.   Freed heap region:       fd
    
66.   Stack left redzone:      f1
    
67.   Stack mid redzone:       f2
    
68.   Stack right redzone:     f3
    
69.   Stack after return:      f5
    
70.   Stack use after scope:   f8
    
71.   Global redzone:          f9
    
72.   Global init order:       f6
    
73.   Poisoned by user:        f7
    
74.   Container overflow:      fc
    
75.   Array cookie:            ac
    
76.   Intra object redzone:    bb
    
77.   ASan internal:           fe
    
78.   Left alloca redzone:     ca
    
79.   Right alloca redzone:    cb
    
80.   Shadow gap:              cc
    
81. ==989484==ABORTING
    
82. $
    

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傻眼貓咪

人造人 发表于 2022-3-6 14:34

我的 gcc 报错机制可能如你所说的没有开启吧，每次我都要设断点才能查看我的内存，哈哈 。
没有关系，我已经下载 Clang 插件了，随时可以更换 Clang 或 gcc。
Clang 测试成功

人造人

傻眼貓咪 发表于 2022-3-6 14:46
我的 gcc 报错机制可能如你所说的没有开启吧，每次我都要设断点才能查看我的内存，哈哈 。
...

windows就不知道了，我没有在windows中用过gcc的内存检查
换linux吧，^_^