c语言中的i/o_C语言中的基本I / O概念

c语言中的i/o

C is a small language, and the “core” of C does not include any Input/Output (I/O) functionality.

C是一个小的语言和“核心” Ç不包括任何输入/输出(I / O)功能。

This is not something unique to C, of course. It’s common for the language core to be agnostic of I/O.

当然，这不是C独有的。 语言核心通常与I / O无关。

In the case of C, Input/Output is provided to us by the C Standard Library via a set of functions defined in the stdio.h header file.

对于C语言，C标准库通过stdio.h头文件中定义的一组函数为我们提供了输入/输出。

You can import this library using:

您可以使用以下命令导入该库：

#include <stdio.h>

on top of your C file.

在您的C文件之上。

This library provides us, among many other functions:

该库为我们提供了许多其他功能：

• printf()

  printf()

• scanf()

  scanf()

• sscanf()

  sscanf()

• fgets()

  fgets()

• fprintf()

  fprintf()

Before describing what those functions do, I want to take a minute to talk about I/O streams.

在描述这些功能之前，我想花一点时间讨论一下I / O流 。

We have 3 kinds of I/O streams in C:

我们在C中有3种I / O流：

• stdin (standard input)

  stdin (标准输入)

• stdout (standard output)

  stdout (标准输出)

• stderr (standard error)

  stderr (标准错误)

With I/O functions we always work with streams. A stream is a high level interface that can represent a device or a file. From the C standpoint, we don’t have any difference in reading from a file or reading from the command line: it’s an I/O stream in any case.

使用I / O功能，我们始终可以处理流。 流是可以代表设备或文件的高级接口。 从C的角度来看，从文件读取或从命令行读取没有任何区别：无论如何，它都是I / O流。

That’s one thing to keep in mind.

这是要记住的一件事。

Some functions are designed to work with a specific stream, like printf(), which we use to print characters to stdout. Using its more general counterpart fprintf(), we can specify the stream to write to.

一些函数被设计为与特定的流一起使用，例如printf() ，我们将其用于将字符打印到stdout 。 使用更通用的对应fprintf() ，我们可以指定要写入的流。

Since I started talking about printf(), let’s introduce it now.

自从我开始谈论printf()以来，现在让我们对其进行介绍。

printf() (printf())

printf() is one of the first functions you’ll use when learning C programming.

printf()是学习C编程时要使用的第一个功能之一。

In its simplest usage form, you pass it a string literal:

在最简单的用法形式中，您为它传递一个字符串文字：

printf("hey!");

and the program will print the content of the string to the screen.

然后程序会将字符串的内容打印到屏幕上。

You can print the value of a variable, and it’s a bit tricky because you need to add a special character, a placeholder, which changes depending on the type of the variable. For example we use %d for a signed decimal integer digit:

您可以打印变量的值，这有点棘手，因为您需要添加一个特殊字符(占位符)，该字符会根据变量的类型而变化。 例如，我们将%d用于带符号的十进制整数：

int age = 37;

printf("My age is %d", age);

We can print more than one variable by using commas:

我们可以使用逗号来打印多个变量：

int age_yesterday = 37;
int age_today = 36;

printf("Yesterday my age was %d and today is %d", age_yesterday, age_today);

There are other format specifiers like %d:

还有其他格式说明符，例如%d ：

• %c for a char

  %c个字符

• %s for a char

  %s为一个字符

• %f for floating point numbers

  %f用于浮点数

• %p for pointers

  %p的指针

and many more.

还有很多。

We can use escape characters in printf(), like \n which we can use to make the output create a new line.

我们可以在printf()使用转义字符，例如\n ，以便使输出创建新行。

scanf() (scanf())

printf() is used as an output function. I want to introduce an input function now, so we can say we can do all the I/O thing: scanf().

printf()用作输出函数。 我现在想介绍一个输入函数，因此可以说我们可以完成所有I / O事情： scanf() 。

This function is used to get a value from the user running the program, from the command line.

此函数用于从运行命令行的用户那里获取值。

We must first define a variable that will hold the value we get from the input:

我们必须首先定义一个变量，该变量将保存从输入中获得的值：

int age;

Then we call scanf() with 2 arguments: the format (type) of the variable, and the address of the variable:

然后我们用两个参数调用scanf() ：变量的格式(类型)和变量的地址：

scanf("%d", &age);

If we want to get a string as input, remember that a string name is a pointer to the first character, so you don’t need the & character before it:

如果要获取字符串作为输入，请记住字符串名称是第一个字符的指针，因此您不需要在&字符之前：

char name[20];
scanf("%s", name);

Here’s a little program that uses both printf() and scanf():

这是一个同时使用printf()和scanf()的小程序：

#include <stdio.h>

int main(void) {
  char name[20];
  printf("Enter your name: ");
  scanf("%s", name);
  printf("you entered %s", name);
}

Download my free C Handbook, and check out my premium Courses

下载我的免费C手册 ，并查看我的高级课程

翻译自: https://flaviocopes.com/c-input-output/

c语言中的i/o