introduction
Standard input and output (Standard I/O) in computer systems is a concept we often encounter in daily programming and system development. This article will comprehensively introduce the concept of standard input and output, how to use it, and some related important concepts and techniques.
What is standard input and output?
Standard input and output refers to the way in which computer programs interact with external environments (such as terminals, files, etc.). In Unix and Unix-like systems, standard input and output are called stdin, stdout, and stderr. Among them, stdin is used to receive input data, stdout is used to output normal information, and stderr is used to output error information.
standard input
Standard input is one of the ways that a program obtains data from the external environment. Through standard input, we can interact with users and receive information entered by users. In Unix systems, the keyboard is usually used as the standard input device.
In most programming languages, we can use the corresponding API functions to obtain data from standard input. For example, in C language, we can use scanffunctions to read data from standard input. Here is a simple example:
#include <stdio.h>
int main() {
int num;
printf("请输入一个整数：");
scanf("%d", &num);
printf("您输入的整数是：%d\n", num);
return 0;
}
In the above code, we scanfread the integer input by the user through the function and store it in numthe variable, and then printfoutput the input integer to the terminal through the function.
In addition to C language, other programming languages such as Python, Java, etc. also provide corresponding standard input functions and classes.
stdout
Standard output is one of the ways that a program outputs results to the external environment. Through standard output, we can display calculation results, prompt information, etc. to the user. In Unix systems, the terminal is usually used as the standard output device.
Similar to standard input, most programming languages provide output functions or classes for us to use. For example, in Python, we can use printfunctions to output information. Here is a simple example:
num = input("请输入一个整数：")
print("您输入的整数是：" + num)
In the above code, we inputobtain the integer entered by the user through a function and store it in numa variable, and then printoutput the entered integer to the terminal through the function.
It should be noted that the usage and characteristics of output functions may be different in different programming languages. For example, some languages' output functions automatically wrap lines, while other languages require manually adding line breaks.
standard error output
Standard error output is one of the ways a program outputs error information when an error occurs. Through standard error output, we can display error prompt information to users to help them locate and solve problems.
Similar to standard output, most programming languages provide corresponding error output functions or classes. For example, in Java, we can use System.err.printlnfunctions to output error messages. Here is a simple example:
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("请输入一个整数：");
int num;
try {
num = scanner.nextInt();
System.out.println("您输入的整数是：" + num);
} catch (Exception e) {
System.err.println("输入错误，请重新输入整数！");
}
}
}
In the above code, we Scannerobtain the integer entered by the user through the class and try to convert it to an integer type. If the user input is not an integer, an exception will be generated, and then we System.err.printlnwill output the error message through the function.
file redirection
In addition to interacting with the terminal, we can also redirect standard input and output through files. In Unix and Unix-like systems, we can use symbols <and >to implement file redirection.
Specifically, <symbols are used to specify the source file for standard input, while >symbols are used to specify the destination file for standard output. For example, we can save the output of a program to a file, or read data from a file as input to the program.
Here is an example:
# 将文件input.txt的内容作为程序的标准输入
./program < input.txt
# 将程序的标准输出保存到文件output.txt
./program > output.txt
# 将文件input.txt的内容作为程序的标准输入，并将程序的标准输出保存到文件output.txt
./program < input.txt > output.txt
Through file redirection, we can easily perform batch processing, automated testing and other operations on the program.
Conclusion
This article comprehensively introduces the concept and use of standard input and output in computer systems. We discussed the meaning and usage techniques of standard input, standard output, and standard error output in detail, and briefly introduced the use of file redirection. By in-depth understanding and flexible use of standard input and output, we can better write high-quality computer programs and systems.