C language advanced (a) — data storage

The article directories

• • 1. Detailed introduction of data types
  • 1. Basic built-in types of C
  • Types of C language:
  • 2. Meaning of type:
  • 3. Basic classification of types
  • The storage of integer types in memory
  • 1. How is the data stored in the allocated memory?
  • 2. Why is complement stored in memory?
  • 3. How to store a and B in the memory
  • 4. Introduction to the big and small ends
  • 5. Causes of the large and small end
  • 5. 6. Smart water bottle
  • Floating-point storage in memory
  • 1. The representation of floating point numbers
  • 2. Floating point type stores the form in memory
  • End of chapter!!

1. Detailed introduction of data types

1. Basic built-in types of C

Types of C language:

1. Built-in types



2. Custom types (constructed types)

2. Meaning of type:

int main(a)
{
	int a = 10;
	float b = 10.0;
	return 0;
}
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3. Basic classification of types

(1) Plastic surgery family

Why does Char belong to the plastic surgery family?

Char is a character type, which is hard to classify, and characters are stored in memory as Ascll code values. Ascll code values are integers, and characters are also stored as integers, so they belong to the plastic family

Unsigned how does signed describe signed without sign?

Take the char type as an example:

Signed (signed)

A signed number with the highest sign bit. (0 – + 1—- +)

Unsigned

An unsigned number with no sign bits

11111111 corresponds to 255

(2) Family of floating point types

(3) Construct type (custom type)

(4) Pointer type

(5) Empty type

Often used for functions, void is used for functions that do not require a return value, and where a return type is used, it can be used for the parameters of the function.

The next section focuses on the memory storage of integers and floating-point types

The storage of integer types in memory

1. How is the data stored in the allocated memory?

Such as:

int a = 20;
int b = - 10;
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We all know that A allocates 4 bytes, so how does A store it?

Here we need to understand the following concepts:

Through debugging, we know the contents of a and B stored in memory, so how do A and B convert such data?

The binary conversion of A and B is carried out. The complement codes are stored in memory and the complement codes of A and B are calculated

Ok, so when we get the complement, the memory is displaying hexadecimal numbers, and we convert the complement to hexadecimal,

Using the binary to hexadecimal rule, every four bits are represented by a hexadecimal number

So we come to a conclusion: for orthopedics, the data store memory actually holds the complement.

\

2. Why is complement stored in memory?

int main(a)
{

	int a = 1;
	int b = - 1;
	int c = 1 - 1;
    return 0; }Copy the code

3. How to store a and B in the memory

We can see that a and B store their complement, but not in the right order. Why is that? \

4. Introduction to the big and small ends

5. Causes of the large and small end

Why are there big and small ends?

Knowing the concept of size, we should know that our machines use small-endian storage, which is why we store backwards.

Take this opportunity to learn something about both the big and the small

5. 6. Smart water bottle

#include <stdio.h>
int check_sys(a)
{
 int i = 1;
 return(* (char *)&i);
}
int main(a)
{
 int ret = check_sys();
 if(ret == 1)
 {
 printf("Little end \ n");
 }
 else
 {
 printf("The big end \ n";)
 }
 return 0;
 }
Copy the code

Floating-point storage in memory

\

1. The representation of floating point numbers

2. Floating point type stores the form in memory

\

There are also the following specific rules for the significant number M stored in memory:

1.0 <= M < 2.0, M can be written as 1. XXXXX, where XXXX is the decimal part

For example, 5. 0 is 1.01 * 2 ^ 2. The significant digit is 1.01.





M out of

Of course, when you take a significant digit out of memory, remember to take out the decimal place of the significant digit, and automatically fill in the decimal place with 1.







With the exponent E, the situation is more complicated





E is stored in memory











Take the 8-bit E for example

Take 0.5 in decimal

0.5 is converted to binary to 0.1

0.1

1.0 times 2 to the minus 1.

So E is negative 1, negative, but E is an unsigned integer.

So when we store E in memory, we need a middle number, and for 8-bit E, the middle number is 127, so we actually store E in memory = -1 + 127 = 126.

\

E gets out of memory

All E is not 0 or all E is not 1, which is the normal situation. You only need to change e-127 to get the real E.

When E is all 0, if E + 127 = 0, then true E = -127, a number to the -127 power is approximately 0, so what we get is a number that is infinitely close to 0 (almost non-existent), so IEE754 states, E = 1-127 or E = 1-1023 is the true value, the significant digit does not add the first 1, directly +/ -0. XXXX * 2^(-126).

E is all 1s, resulting in +/- 1.xxxx * 2 ^ (128), a number representing plus or minus infinity. So much for storing integer and floating point types in memory. I hope you can practice a lot and be familiar with the rules of storing these two types in memory. \

Thank you ！！！！

End of chapter!!