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Preliminary: VS Debugging Tips
(1), there is a piece of code to be debugged.
#include<stdio.h>
int main() {
int a = 10;
float b = 10.0f;
return 0;
}
(2), there is a breakpoint.
Just click there.
(3), enter debugging.
Effect: run, but not displayed.
(4), bring up the memory interface.
Debug - Window - Memory - choose any one.
Effect:
(5), check the value of a variable.
Enter &xxx in the address and press Enter. xxx is the variable name.
In the case, the value of a is 10, the memory is 0a, hexadecimal. a is 1 greater than 9, which is 10.
1, 1 and -1 memory
Code for debugging:
#include<stdio.h>
int main() {
int a = 1;
int b = -1;
return 0;
}
Memory result: 1
Memory result: -1
No doubt, it is the four bytes in the upper left corner.
2, signed, unsigned
Values use the highest binary bit to represent the sign. 0 is positive, 1 is negative.
An unsigned modified type has no sign bit.
For example, unsigned int, four bytes, are all numeric content.
In int, the highest bit represents the sign, and only 31 bits are numeric.
Unsigned max:
n-1 of 2 signed max: n-1 of 2-1
3, original code, inverse code, complement code
Unsigned number: The three codes are the same.
Signed positive number: The three codes are the same.
Signed Negative Numbers: Pay attention.
Source code: The binary representation of a numerical value.
One's complement: the sign remains unchanged, and the other bits are flipped. 1 becomes 0, 0 becomes 1.
Two's complement: add 1 to the result of one's complement.
Example: -1, one byte.
Original code: 1 000 0001
Inverse code: 1 111 1110
Complement code: 1 111 1111
,4, integers are stored in two's complement
The three codes of 1 are the same, so the byte order of 01 00 00 00 in memory
is reversed.
The complement of -1 is 1111 1111
to hexadecimal, which is ff.
5, complement, positive addition
Just add it directly.
1+1=2
0000 0001
0000 0001
=》
0000 0010
6, complement, subtraction of positive numbers
Convert to positive and negative numbers, and add directly.
-1
Original: 1000 0001
Anti: 1111 1110
Complement: 1111 1111
1±1=0
0000 0001 + 1111 1111
Sign bit: 1
Value: 000 0000, overflow.
On overflow, the sign bit is flipped, the result:
0000 0000
7, big endian, little endian
There are two strategies for storing data:
- Play from left to right. 1 is 00 00 00 01
- Play from right to left. 1 is 01 00 00 00
Use the pointer to determine the current policy:
int isSmall() {
int test = 1;
char* p = (char*)&test;
if (*p == 1) {
//大端
return 0;
}
else {
//小端
return 1;
}
}
To simplify:
int isBig() {
int test = 1;
return *(char*)&test;
}
Extra: Realize Modify Money
Change an address value to ff.
Code:
#include<stdio.h>
int main() {
int money = 10;
printf("金币数：%d\n", money);
printf("金币数：%d\n",money);
return 0;
}
Find the memory address of money:
Right-click on the value to edit the value.
Effect:
Final display:
