Read an article. Bowen , which is described as follows

 1 #include <stdio.h>  
 2   
 3 int main()  
 4 {  
 5     unsigned short a = 1;  
 6     unsigned short b = 0;  
 7    
 8     if (a < (b-1)) //a and b-1 Result-1 All converted to int Type comparison, 1<-1，Obviously false  
 9     {  
10         printf("in if\n");  
11     }  
12   
13     return 0;  
14       
15 }  

The expected result prints "in if", but the actual run time finds nothing to output. Change to the following code to output "in if" as expected

 1 #include <stdio.h>  
 2   
 3 int main()  
 4 {  
 5     unsigned short a = 1;  
 6     unsigned int b = 0;  
 7    
 8     if (a < (b-1)) //b-1 Result-1，Converted to 0 xffffffff，1<0xffffffff，Obviously true ah  
 9     {  
10         printf("in if\n");  
11     }  
12   
13     return 0;  
14       
15 }  

Use assembly to directly compare the results of the two (company security does not allow sending Internet pictures..), and find the main differences in the following 5 lines. In the first four lines, the short is extended from 2 bytes to 4 bytes, and the high bit is filled with 0. The reason why the running result does not conform to the expectation is in line 5: jge 8048461

 1 08048425 <main>:
 2  8048425:      8d 4c 24 04              lea    0x4(%esp),%ecx
 3  8048429:      83 e4 f0                 and    $0xfffffff0,%esp
 4  804842c:      ff 71 fc                 pushl  -0x4(%ecx)
 5  804842f:      55                       push   %ebp
 6  8048430:      89 e5                    mov    %esp,%ebp
 7  8048432:      51                       push   %ecx
 8  8048433:      83 ec 14                 sub    $0x14,%esp
 9  8048436:      66 c7 45 f6 01 00        movw   $0x1,-0xa(%ebp)
10  804843c:      66 c7 45 f4 00 00        movw   $0x0,-0xc(%ebp)
11  8048442:      0f b7 45 f6              movzwl -0xa(%ebp),%eax
12  8048446:      0f b7 55 f4              movzwl -0xc(%ebp),%edx
13  804844a:      83 ea 01                 sub    $0x1,%edx
14  804844d:      39 d0                    cmp    %edx,%eax
15  804844f:      7d 10                    jge    8048461 <main+0x3c>
16  8048451:      83 ec 0c                 sub    $0xc,%esp
17  8048454:      68 00 85 04 08           push   $0x8048500
18  8048459:      e8 a2 fe ff ff           call   8048300 <puts@plt>
19  804845e:      83 c4 10                 add    $0x10,%esp
20  8048461:      b8 00 00 00 00           mov    $0x0,%eax
21  8048466:      8b 4d fc                 mov    -0x4(%ebp),%ecx
22  8048469:      c9                       leave  
23  804846a:      8d 61 fc                 lea    -0x4(%ecx),%esp
24  804846d:      c3                       ret    
25  804846e:      66 90                    xchg   %ax,%ax

The values in the assembly are not signed, but the instructions are signed. The jge used above is a signed comparison method, resulting in a comparison result of: if (1 < - 1), false, and no string will be printed