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This article mainly introduces "how C language data is stored in memory". In daily operation, I believe many people have doubts about how C language data is stored in memory. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful for you to answer the question of "how C language data is stored in memory". Next, please follow the editor to study!

Detailed introduction of data types

In the previous overview of the basic C language, the basic C language built-in types have been mentioned, but there are countless C data types, but these types can be divided into several broad categories:

Classification of types:

Saving integers

Char,short,int,long,long long and its supporting unsigned,int*,int []...

two。 Storage of floating point numbers

Float,double,float []...

Structure (the storage of the structure in memory will be discussed later)

Storage of integer memory species:

1. Byte order

two。 Complement code

Memory window

The memory window in debug mode cannot be opened if it is not debugged. Under normal circumstances, without debugging, there is no memory window.

Char str [] = "abc"

Here, only part of the image of the memory data is captured, so it is easy to observe clearly.

There are a lot of "cc cc cc" in memory data, that is, 0xcc. In fact, the interrupt instruction is expressed in the CPU of Intel. In the debug mode of VS, the back of the local variable is filled with 0xcc. The purpose of filling is to find the subscript out of bounds in time.

Int num = 0x11223344

Byte order is involved here.

Byte order

Byte order is in bytes

Byte order is divided into big-end byte order (big-end order) and small-end byte order (small-end order).

Big-end byte order: put the status on the high address

Small end byte order: that is to put the low order (small) on the low address (small) (small)

Generally speaking, the small end sequence is more widely used. Byte order is an attribute related to CPU. The CPU of Intel is mainly small end order.

The above example: if the 0x11223344 memory data is 11223344, it is a large end order, and 44332211 is a small end order.

Does the program judge the big end sequence or small end sequence?

Int isBidEnd () {int num = 0x11223344; int* p = & num; char* p2 = (char*) p; if (* p2 = = 0x11) {return 1;} else {return 0;}} int main () {int ret = isBidEnd () If (ret = = 1) {printf ("large end sequence\ n");} else {printf ("small end order\ n");} system ("pause"); return 0;}

The forced type conversion between pointers will not affect the address value stored inside the pointer, but only the dereferencing operation of the subsequent order.

The byte order of network transmission is fixed using the big end ~

Complement code

Plastic storage in memory: original code, inverse code, complement code

Original code: set the symbol bit to 1 on the basis of the binary of a positive number

Inverse code: the symbol bit is unchanged, and the other bits are inverted ~

Complement: inverse code + 1, you can get the complement.

The original, inverse and complement of positive numbers are all the same.

For example:

Int main () {char a =-1; signed char b =-1. There is no difference between unsigned char pause and signed char. Unsigned char c =-1; printf ("a% d\ nb=%d\ nc=%d\ n", a, b, c); system ("pause"); return 0;}

Rules for type conversion

1. Convert long data into short data, and truncate the high data directly.

two。 Change the short data into the growth data, and the high position needs to be filled with sign bits.

Floating-point storage in memory

The calculation of decimals in computers is much more complicated than integers.

Floating point storage rules:

IEEE754 stipulates that:

For 32-bit floating-point numbers:

The highest bit is the symbol bit s, the next 8 bits are exponent E, and the remaining 23 bits are significant digits M.

For 64-bit floating-point numbers:

The highest bit is the symbol bit S, the next 11 bits are the exponent E, and the remaining 52 bits are the valid array M.

A floating point number in the computer is expressed by the way of "scientific counting" ~ expressed by how many powers of 2.

2 ^ E (2 to the power of E)

The larger the E, the larger the range of data that can be represented.

The larger the M, the higher the accuracy of the data that can be represented.

Therefore, priority is given to the use of double

At this point, the study of "how C language data is stored in memory" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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