Что такое стандарт POSIX и как он влияет на операционные системы

The Portable Operating System Interface (POSIX) is a set of standards that define how operating system APIs should behave in order to ensure interoperability between different Unix-like systems. POSIX specifies a set of interfaces, utilities, and conventions that applications can use to access system resources, such as files, directories, processes, and signals. The use of POSIX standards makes it easier for developers to write portable code that works across different Unix variants, and it also allows users to migrate their applications and data from one system to another without having to change their software.

POSIX standards are maintained by the IEEE Standards Association, which has several working groups that define specifications for different aspects of operating system functionality. Some of the most important POSIX standards include:

POSIX.1 - defines the core API and shell interface for interacting with the operating system, including process management, file operations, environment variables, and signals. This standard also defines the shell language used in Unix/Linux shells.
POSIX.2 - adds more standard utilities and tool commands to the system, such as awk, sed, and regex.
POSIX.4 - includes real-time extensions, which allow applications to control and manage the timing of their execution and the scheduling of system resources.
POSIX.9 - defines APIs for accessing the network capabilities of a system, such as sockets and remote procedure calls.

Developers can use POSIX-compliant APIs in their programs by including the appropriate header files and linking their applications with POSIX libraries. For example, to use the POSIX file I/O API, a developer might include the and headers and link their code with the POSIX-compliant libc library.

Here's an example program that uses POSIX file I/O to write a message to a file:


#include 
#include 
#include 
int main() {
    int fd = open("message.txt", O_WRONLY | O_CREAT, 0666);
    if (fd == -1) {
        perror("open");
        return 1;
    }
    const char *message = "Hello, POSIX!";
    if (write(fd, message, strlen(message)) == -1) {
        perror("write");
        return 1;
    }
    close(fd);
    return 0;
}

In this program, the `open` function is called with the file name "message.txt" and a set of flags that specify that it should be opened for writing (`O_WRONLY`) and created if it doesn't exist (`O_CREAT`). The `0666` argument specifies the file permissions.

Next, the program writes a message to the file using the `write` function, which takes the file descriptor returned by `open`, a pointer to the message, and the length of the message in bytes. If an error occurs, `write` returns -1 and sets the global `errno` variable to indicate the type of error that occurred.

Finally, the program closes the file descriptor returned by `open` to release the system resources associated with the file.

This is just one example of how POSIX-compliant APIs can be used to write portable code on Unix-like systems. By following the POSIX standards, developers can ensure that their applications will work correctly on a variety of different systems and provide a consistent user experience.

Что такое стандарт POSIX и как он влияет на операционные системы

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