未定义的行为 [英] Undefined Behavior
问题描述
为什么这段代码会导致未定义的行为？
#include< stdio.h>
#include< stdlib.h>
#include< string.h>
#define TRUE 1
#define FALSE 0
＃ define MAX_PASSWORD 11
int loop;
unsigned char rx;
int _strlen（s）
unsigned char s [];
{
int i;
i = 0;
while（s [我]！=''\'''）
++我;
返回i;
}
int encrypt（s，x，len）
unsigned char * s;
unsigned char x;
int len ;
{
int i，ok;
unsigned char seed_1，seed_2;
seed_1 = rx;
seed_2 = rx + 31;
ok = TRUE;
for（i = 0; i< len; i ++）
{
seed_1 - = i;
seed_2 + = i;
if（i ％2！= 0）
s [i] - = seed_1;
else
s [i] + = seed_2;
if（s [i] ==''&''|| s [i] ==''\ 0''|| s [i] ==''\ n''）
ok = FALSE;
}
if（x =='' &''）
ok = FALSE;
返回ok;
}
int decrypt（s，len）
unsigned char * s;
int len;
{
unsigned char seed_1，seed_2;
int i;
seed_1 = rx;
seed_2 = rx + 31;
for（i = 0; i< len; i ++）
{
seed_1 - = i;
seed_2 + = i;
if（i％2！= 0）
s [i] + = seed_1;
else
s [i] - = seed_2;
}
返回TRUE;
}
int encrypt_string（s）
unsigned char * s;
{
unsigned char x;
int c，len;
x = 0;
c = FALSE;
len = _strlen（s）;
while（c！= FALSE || loop> 0）
{
x ++;
c =加密（s，x，len）;
循环 - ;
}
s [len ++] = x;
s [len ++] = rx;
s [len] =''\ 0'';
返回TRUE;
}
int decrypt_string（s）
unsigned char * s;
{
unsigned char x，y;
int len;
len = _strlen（s）-1 ;
rx = s [len];
len--;
x = s [len];
for（y = 0; y< X ; y ++）
解密（s，len）;
s [len] =''\ 0'';
返回是的;
}
int main（）{
unsigned char * s;
unsigned char endchar;
unsigned int y;
int len;
s =（unsigned char *）calloc（MAX_PASSWORD，sizeof（unsigned char）） ;
if（s == NULL）{
printf（无法分配内存）;
返回0;
}
fgets（s，MAX_PASSWORD，stdin）;
len = _strlen（s）;
endchar = s [len-1];
if（endchar ==''\ r''|| endchar ==''\ n''）
s [len-1] =''\ 0'';
rx = strlen（s）;
循环= 1;
y = encrypt_string（s）;
if（y == TRUE）
printf（ " \\\
\\\
Encrypted String：％s ######％d \ n \ nn"，s，_strlen（s））;
y = decrypt_string （s）;
if（y == TRUE）
printf（" De crypted String：％s％d \ n"，s，_strlen（s））;
if（* s =！NULL）{
免费（s）;
s = NULL;
}
else
printf（"无法解除分配内存\\ n"）;
返回0;
}
bb****@gmail.com 说：
为什么这段代码会导致未定义的行为？
#include< stdio.h>
#include< stdlib.h>
#include< string.h>
#define TRUE 1
#define FALSE 0
＃ define MAX_PASSWORD 11
int loop;
unsigned char rx;
int _strlen（s）
入侵实现名称空间。
-
Richard Heathfield
Usenet是一个奇怪的地方 - dmr 29/7/1999
http://www.cpax.org.uk
电子邮件：rjh在上述域名中， - www。
在文章< 11 ******* ***************@r35g2000prh.googlegroups .com> ;,
< bb **** @ gmail.comwrote：
> #define MAX_PASSWORD 11
s =（unsigned char *）calloc（MAX_PASSWORD，sizeof（unsigned char） ）;
if（s == NULL）{
printf（无法分配内存）;
返回0;
}
fgets（s，MAX_PASSWORD，stdin）;
len = _strlen（s）;
这是什么_strlen（）？除了其他任何东西，这是一个保留的
名称。
>
endchar = s [ len-1];
if（endchar ==''\ r''|| endchar ==''\ n''）
s [LEN-1] = '' \0 '';
所以此时s指向缓冲区中长达11个字节的字符串（包括结尾处的n
）字节长。
y = encrypt_string（s）;
> int encrypt_string（s）
....
s [len ++] = x;
s [len ++] = rx;
s [len] =''\ 0 '';
Woops！你正在添加东西到s的末尾，并且溢出
缓冲区。
你应该能够自己找到这样的错误，使用一个
内存检查工具，如valgrind。
- Richard
-
" ;应考虑在一些字母表中需要多达32个字符
- X3.4,1963。
bb **** @ gmail.com 写道：
>
为什么这段代码会导致未定义的行为？
#include< stdio.h>
#include< stdlib.h>
#include< string.h>
#define TRUE 1
#define FALSE 0
#define MAX_PASSWORD 11
int loop;
unsigned char rx;
int _strlen（s）
unsigned char s [];
{
因为在这里你使用了为
实现保留的标签。不要那样做。
-
< http://www.cs.auckland.ac.nz/~pgut001/pubs/ vista_cost.txt>
< http://www.securityfocus.com/columnists/423>
< http://www.aaxnet.com/editor/ edit043.html>
cbfalconer at maineline.net
-
通过 http://www.teranews.com
Why would this code cause undefined behavior?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define TRUE 1
#define FALSE 0
#define MAX_PASSWORD 11
int loop;
unsigned char rx;
int _strlen(s)
unsigned char s[];
{
int i;
i=0;
while(s[i]!=''\0'')
++i;
return i;
}
int encrypt (s, x, len)
unsigned char *s ;
unsigned char x;
int len;
{
int i,ok;
unsigned char seed_1,seed_2;
seed_1 = rx;
seed_2 = rx + 31;
ok = TRUE;
for(i = 0 ; i < len ; i++)
{
seed_1 -= i;
seed_2 += i;
if(i%2 != 0)
s[i] -= seed_1;
else
s[i] += seed_2;
if(s[i] == ''&'' || s[i]== ''\0'' || s[i] == ''\n'')
ok = FALSE;
}
if (x == ''&'')
ok = FALSE;
return ok;
}
int decrypt (s, len)
unsigned char *s;
int len ;
{
unsigned char seed_1, seed_2;
int i;
seed_1 = rx;
seed_2 = rx+31;
for (i = 0; i < len ; i++)
{
seed_1 -= i;
seed_2 +=i;
if (i % 2 != 0)
s[i] += seed_1;
else
s[i] -= seed_2;
}
return TRUE;
}
int encrypt_string (s)
unsigned char *s ;
{
unsigned char x;
int c, len;
x=0;
c=FALSE;
len= _strlen(s);
while( c!= FALSE || loop>0)
{
x++;
c=encrypt(s, x, len);
loop--;
}
s[len++] = x;
s[len++] = rx;
s[len]= ''\0'';
return TRUE;
}
int decrypt_string(s)
unsigned char *s;
{
unsigned char x,y ;
int len;
len = _strlen(s)-1;
rx= s[len];
len--;
x=s[len];
for(y = 0; y < x ; y++)
decrypt(s, len);
s[len]= ''\0'';
return TRUE;
}
int main() {
unsigned char *s;
unsigned char endchar;
unsigned int y;
int len;
s=(unsigned char *) calloc( MAX_PASSWORD, sizeof(unsigned char) );
if(s==NULL){
printf("Could not allocate Memory");
return 0;
}
fgets(s,MAX_PASSWORD,stdin);
len=_strlen(s);
endchar =s[len-1];
if(endchar==''\r'' || endchar==''\n'')
s[len-1]=''\0'';
rx=strlen(s) ;
loop=1;
y=encrypt_string(s);
if(y==TRUE)
printf("\n\nEncrypted String :%s ######%d\n\n",s,_strlen(s));
y=decrypt_string(s);
if(y==TRUE)
printf("Decrypted String: %s %d\n",s,_strlen(s));
if(*s=!NULL){
free(s);
s=NULL;
}
else
printf("Could not deallocate memory\n");
return 0;
}
bb****@gmail.com said:
Why would this code cause undefined behavior?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define TRUE 1
#define FALSE 0
#define MAX_PASSWORD 11
int loop;
unsigned char rx;
int _strlen(s)Invading implementation namespace.
--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at the above domain, - www.
In article <11**********************@r35g2000prh.googlegroups .com>,
<bb****@gmail.comwrote:
>#define MAX_PASSWORD 11
s=(unsigned char *) calloc( MAX_PASSWORD, sizeof(unsigned char) );
if(s==NULL){
printf("Could not allocate Memory");
return 0;
}
fgets(s,MAX_PASSWORD,stdin);
len=_strlen(s);What''s this _strlen()? Apart from anything else, that''s a reserved
name.
>
endchar =s[len-1];
if(endchar==''\r'' || endchar==''\n'')
s[len-1]=''\0'';So at this point s points to a string up to 11 bytes long (including
the nul at the end) in a buffer 11 bytes long.
y=encrypt_string(s);
>int encrypt_string (s)....
s[len++] = x;
s[len++] = rx;
s[len]= ''\0'';Woops! You''re adding things on to the end of s, and overflowing the
buffer.
You should be able to find mistakes like this yourself, using a
memory checking tool such as valgrind.
-- Richard
--
"Consideration shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963.
bb****@gmail.com wrote:>
Why would this code cause undefined behavior?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define TRUE 1
#define FALSE 0
#define MAX_PASSWORD 11
int loop;
unsigned char rx;
int _strlen(s)
unsigned char s[];
{Because right here you have used a label reserved for the
implementation. Don''t do that.
--
<http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfocus.com/columnists/423>
<http://www.aaxnet.com/editor/edit043.html>
cbfalconer at maineline.net
--
Posted via a free Usenet account from http://www.teranews.com
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