Cprogramming 简明教程

C - Data Types

C 中的 _ Data types _ 引用了用于声明不同类型 _ variables _ 或 _ functions _ 的一个广泛系统。变量的类型决定了它在存储中占据多少空间，以及如何解释存储的位模式。在本章中，我们将了解 _ data types in C _。一个相关概念是“变量”，它指的是处理器内存中的可寻址位置。通过不同的输入设备获取的数据存储在计算机内存中。一个符号名称可以分配给称为变量名的存储位置。

Data types in C refer to an extensive system used for declaring variables or functions of different types. The type of a variable determines how much space it occupies in storage and how the bit pattern stored is interpreted. In this chapter, we will learn about data types in C. A related concept is that of "variables", which refer to the addressable location in the memory of the processor. The data captured via different input devices is stored in the computer memory. A symbolic name can be assigned to the storage location called variable name.

C 是一种静态类型语言。变量的名称及其打算存储的数据类型必须在实际使用之前明确声明。

C is a statically typed language. The name of the variable along with the type of data it intends to store must be explicitly declared before actually using it.

C 也是强类型语言，这意味着不允许将一种数据类型自动或隐式转换为另一种数据类型。

C is also a strongly typed language, which means that the automatic or implicit conversion of one data type to another is not allowed.

C 中的数据类型可以分类如下：

The types in C can be classified as follows −

Sr.No.	Types & Description
1	Basic Types They are arithmetic types and are further classified into: (a) integer types and (b) floating-point types.
2	Enumerated types They are again arithmetic types and they are used to define variables that can only assign certain discrete integer values throughout the program.
3	The type void The type specifier void indicates that no value is available.
4	Derived types They include (a) Pointer types, (b) Array types, (c) Structure types, (d) Union types and (e) Function types.

数组类型和结构类型统称为聚合类型。函数的类型指定了函数返回值的类型。我们将在下一部分中看到基本类型，而其他类型将在即将到来的章节中进行介绍。

The array types and structure types are referred collectively as the aggregate types. The type of a function specifies the type of the function’s return value. We will see the basic types in the following section, where as other types will be covered in the upcoming chapters.

Integer Data Types in C

下表提供了标准整数类型及其存储大小和值范围的详细信息：

The following table provides the details of standard integer types with their storage sizes and value ranges −

Type

Storage size

Value range

char

1 byte

-128 to 127 or 0 to 255

unsigned char

1 byte

0 to 255

signed char

1 byte

-128 to 127

int

2 or 4 bytes

-32,768 to 32,767 or -2,147,483,648 to 2,147,483,647

unsigned int

2 or 4 bytes

0 to 65,535 or 0 to 4,294,967,295

short

2 bytes

-32,768 to 32,767

unsigned short

2 bytes

0 to 65,535

long

8 bytes

-9223372036854775808 to 9223372036854775807

unsigned long

8 bytes

0 to 18446744073709551615

要获取特定平台上类型或变量的确切大小，可以使用 sizeof 运算符。表达式 sizeof(type) 会生成对象或类型的存储大小（以字节为单位）。

To get the exact size of a type or a variable on a particular platform, you can use the sizeof operator. The expressions sizeof(type) yields the storage size of the object or type in bytes.

Example of Integer Data Types

下面是使用 limits.h 头文件中定义的不同常数在机器上获取各种类型大小的示例：

Given below is an example to get the size of various type on a machine using different constant defined in limits.h header file −

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <float.h>

int main(int argc, char** argv) {

   printf("CHAR_BIT    :   %d\n", CHAR_BIT);
   printf("CHAR_MAX    :   %d\n", CHAR_MAX);
   printf("CHAR_MIN    :   %d\n", CHAR_MIN);
   printf("INT_MAX     :   %d\n", INT_MAX);
   printf("INT_MIN     :   %d\n", INT_MIN);
   printf("LONG_MAX    :   %ld\n", (long) LONG_MAX);
   printf("LONG_MIN    :   %ld\n", (long) LONG_MIN);
   printf("SCHAR_MAX   :   %d\n", SCHAR_MAX);
   printf("SCHAR_MIN   :   %d\n", SCHAR_MIN);
   printf("SHRT_MAX    :   %d\n", SHRT_MAX);
   printf("SHRT_MIN    :   %d\n", SHRT_MIN);
   printf("UCHAR_MAX   :   %d\n", UCHAR_MAX);
   printf("UINT_MAX    :   %u\n", (unsigned int) UINT_MAX);
   printf("ULONG_MAX   :   %lu\n", (unsigned long) ULONG_MAX);
   printf("USHRT_MAX   :   %d\n", (unsigned short) USHRT_MAX);

   return 0;
}

当您编译并执行上述程序时，它会针对 Linux 生成以下结果：

When you compile and execute the above program, it produces the following result on Linux−

CHAR_BIT    :   8
CHAR_MAX    :   127
CHAR_MIN    :   -128
INT_MAX     :   2147483647
INT_MIN     :   -2147483648
LONG_MAX    :   9223372036854775807
LONG_MIN    :   -9223372036854775808
SCHAR_MAX   :   127
SCHAR_MIN   :   -128
SHRT_MAX    :   32767
SHRT_MIN    :   -32768
UCHAR_MAX   :   255
UINT_MAX    :   4294967295
ULONG_MAX   :   18446744073709551615
USHRT_MAX   :   65535

Floating-Point Data Types in C

下表提供了标准浮点类型及其存储大小、值范围和精度的详细信息：

The following table provides the details of standard floating-point types with storage sizes and value ranges and their precision −

Type

Storage size

Value range

Precision

float

4 byte

1.2E-38 to 3.4E+38

6 decimal places

double

8 byte

2.3E-308 to 1.7E+308

15 decimal places

long double

10 byte

3.4E-4932 to 1.1E+4932

19 decimal places

头文件 "float.h" 定义了允许您在程序中使用这些值和其他有关实数二进制表示形式的详细信息的宏。

The header file "float.h" defines the macros that allow you to use these values and other details about the binary representation of real numbers in your programs.

Example Floating-Point Data Types

以下示例打印了浮点类型占用的存储空间及其范围值：

The following example prints the storage space taken by a float type and its range values −

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <float.h>

int main(int argc, char** argv) {

   printf("Storage size for float : %zu \n", sizeof(float));
   printf("FLT_MAX     :   %g\n", (float) FLT_MAX);
   printf("FLT_MIN     :   %g\n", (float) FLT_MIN);
   printf("-FLT_MAX    :   %g\n", (float) -FLT_MAX);
   printf("-FLT_MIN    :   %g\n", (float) -FLT_MIN);
   printf("DBL_MAX     :   %g\n", (double) DBL_MAX);
   printf("DBL_MIN     :   %g\n", (double) DBL_MIN);
   printf("-DBL_MAX     :  %g\n", (double) -DBL_MAX);
   printf("Precision value: %d\n", FLT_DIG );

   return 0;
}

当您编译并执行上述程序时，它会针对 Linux 生成以下结果：

When you compile and execute the above program, it produces the following result on Linux −

Storage size for float : 4
FLT_MAX      :   3.40282e+38
FLT_MIN      :   1.17549e-38
-FLT_MAX     :   -3.40282e+38
-FLT_MIN     :   -1.17549e-38
DBL_MAX      :   1.79769e+308
DBL_MIN      :   2.22507e-308
-DBL_MAX     :  -1.79769e+308
Precision value: 6

Note: "sizeof" 返回 "size_t"。无符号整数 "size_t" 的类型可能会因平台而异。并且，它可能并非无处不在的长无符号整数。在这种情况下，我们为格式字符串使用 "%zu" 而不是 "%d"。

Note: "sizeof" returns "size_t". The type of unsigned integer of "size_t" can vary depending on platform. And, it may not be long unsigned int everywhere. In such cases, we use "%zu" for the format string instead of "%d".

早期版本的 C 语言中没有布尔型数据。C99 对 ANSI C 的标准化中引入了 _bool 类型，其中零值被视为假，非零值被视为真。

Earlier versions of C did not have Boolean data type. C99 standardization of ANSI C introduced _bool type which treats zero value as false and non-zero as true.

User-defined Data Types in C

有两种由用户定义的数据类型 struct 和 union ，它们由用户使用其他基本数据类型的组合进行定义。

There are two user-defined data types struct and union, that can be defined by the user with the help of the combination of other basic data types.

Struct Data Type

一个独特之处 features of C language 是将不同数据类型的值存储在一个变量中。关键字 struct 和 union 用于派生用户定义的数据类型。例如：

One of the unique features of C language is to store values of different data types in one variable. The keywords struct and union are provided to derive a user-defined data type. For example,

struct student   {
   char name[20];
   int marks, age;
};

Union Data Type

联合是结构的特例，其中联合变量的大小不是各个元素大小的总和，如结构中一样，而是对应于各个元素中最大的大小。因此，一次只能使用其中一个元素。请看以下示例：

A union is a special case of struct where the size of union variable is not the sum of sizes of individual elements, as in struct, but it corresponds to the largest size among individual elements. Hence, only one of elements can be used at a time. Look at following example:

union ab  {
   int a;
   float b;
};

我们将在后面的章节中了解有关结构和联合类型的更多信息。

We shall learn more about structure and union types in a later chapter.

The void Data Type in C

void 类型指定不可用任何值。它用于以下三种情况：

The void type specifies that no value is available. It is used in three kinds of situations −

Sr.No

Types & Description

Function returns as void There are various functions in C that do not return any value or you can say they return void. A function with no return value has the return type as void. For example, void exit (int status);

Function arguments as void There are various functions in C which do not accept any parameter. A function with no parameter can accept a void. For example, int rand(void);

Pointers to void A pointer of type void * represents the address of an object, but not its type. For example, a memory allocation function void *malloc( size_t size ); returns a pointer to void which can be casted to any data type.

Arrays Data Type in C

数组是存储在连续内存位置中具有同一数据类型的多个值的集合。数组的大小用方括号 [] 表示。例如，

An array is a collection of multiple values of same data type stored in consecutive memory locations. The size of array is mentioned in square brackets []. For example,

int marks[5];

可以在声明时对数组进行初始化。要分配的值括在括号中。

Arrays can be initialized at the time of declaration. The values to be assigned are put in parentheses.

int marks[ ]={50,56,76,67,43};

C 还支持多维数组。要了解有关数组的更多信息，请参阅关于 Arrays in C 的章节。

C also supports multi-dimensional arrays. To learn more about arrays, refer to the chapter on Arrays in C.

Pointers Data Type in C

指针是特殊变量，用于存储内存中另一个变量/对象的地址或引用。指针变量的名称前缀为星号 (*)。指针变量的类型和要指向的变量/对象必须相同。

A pointer is a special variable that stores address or reference of another variable/object in the memory. The name of pointer variable is prefixed by asterisk (*). The type of the pointer variable and the variable/object to be pointed must be same.

int x;
int *y;
y = &x;

在此处，“y”是存储变量“x”地址的指针变量，“x”为“int”类型。

Here, "y" is a pointer variable that stores the address of variable "x" which is of "int" type.

指针用于许多不同的目的。文本字符串操作和动态内存分配是某些必须使用指针的过程。在本章教程后面，你可以找到关于 Pointers in C 的详细章节。

Pointers are used for many different purposes. Text string manipulation and dynamic memory allocation are some of the processes where the use of pointers is mandatory. Later in this tutorial, you can find a detailed chapter on Pointers in C.