C Beginners ask questions about data types

char is a fixed-length character type, varchar is a variable-length character type, the char column will delete the tail space when retrieval, the myisam storage engine recommends using a fixed-length data column instead of a variable-length data column, and the memory storage engine currently uses a fixed-length data row to store. The Varchar is recommended for the InnoDB storage engine.

Text or blobs are often used to save large texts. The difference between the two is that blobs can be used to hold binary data such as **, while text can only hold character data. Text and blob values can cause some performance issues, especially when performing a large number of delete operations.

You can use synthetic indexes to improve query performance for large text fields (blobs or text).

Choose the applicable type according to the needs of the program, such as counting four operations within 100, using the int type is enough to deal with it. If the program needs to be more precise, then you need to use floating-point or double-precision type, in short, choose according to your needs.

Use data types in the right way.

There are four basic data types for the C++ language:

integer, the specifier is int;

Character, the descriptor is char;

Floating-point type (also known as real type), the specifier is float (single precision), double (double precision);

Null, with void specifiers, is used for functions and pointers.

In order to meet the needs of various situations, in addition to the void type, the above three types can be preceded by modifiers to change the original meaning.

signed means signed.

unsigned means unsigned.

long means long.

short means short.

All four of the above modifiers are suitable for integers and characters, and only long is also suitable for double-precision floating-point types.

1、short：Modified int, short integer data, can omit the modified int. (Introduced in the K&R period).2、long：

Modified int, long integer data, can omit the modified int. (Introduced in the K&R period).3、long long：Modified int, ultra-long integer data, can omit the modified int.

C99 standard added) <>

4、signed：Decorated integer data, signed data type. (New in C89).5、unsigned：

Decorated integer data, unsigned data types. (Introduced in the K&R period).6、restrict：Used to qualify and constrain pointers, and to indicate that pointers are the initial and only way to access a data object.

C99 standard added) <>

There are five basic data types in the C language: character, integer, single-precision real, double-precision real, and null. Although the length and scope of these types of data vary depending on the type of processor and the implementation of the C compiler, in the case of Bit, an integer is equal to the length of a CPU word, a character is usually a byte, and the exact format of floating-point values depends on the implementation.

C also provides several aggregatetypes, including arrays, pointers, structures, commons (unions), bitfields, and enums. Except VO

In addition to the id type, the base type can be preceded by various modifiers. Modifiers are used to change the meaning of the base type in order to more accurately adapt to the needs of various situations. The modifiers are as follows: