Usage of write function

The prototype of the write function is "ssize_t write(int fd, const void *buf, size_t count);". This function accepts three parameters, namely fd, buf and count. The write function writes count bytes of data from the buffer pointed to by buf to the file or device represented by fd. The function return value is the number of bytes actually written.

The write function is a common function used to write data, and it has corresponding versions in many programming languages. Let me take the write function in C language as an example to explain its usage in detail.

In C language, the prototype of the write function is as follows:

ssize_t write(int fd, const void *buf, size_t count);

This function accepts three parameters:

fd: file descriptor, indicating the file to which data is to be written. or equipment.

buf: A pointer to the buffer to which data is to be written.

count: The number of bytes to be written.

The write function writes count bytes of data from the buffer pointed to by buf to the file or device represented by fd. The function return value is the number of bytes actually written.

The following is a sample code using the write function:

#include <stdio.h>  
#include <unistd.h>  
  
int main() {  
    char message[] = "Hello, world!\n";  
    int fd = open("output.txt", O_WRONLY | O_CREAT, 0644);  // 打开文件，用于写入  
    if (fd == -1) {  
        perror("open");  
        return 1;  
    }  
    ssize_t result = write(fd, message, sizeof(message) - 1);  // 写入数据到文件  
    if (result == -1) {  
        perror("write");  
        return 1;  
    }  
    close(fd);  // 关闭文件  
    return 0;  
}

This code first defines a string message, and then uses the open function to open a file named output.txt for data input. Then use the write function to write the data in message to the file. Finally close the file and return.

It should be noted that the write function is a low-level function that directly operates the file descriptor, so it needs to be used with caution. In some advanced programming languages, more advanced functions or methods for writing data are usually provided, such as the open function and write method in Python, the FileOutputStream class in Java, etc. These advanced functions or methods are usually easier to use and safer, so they are usually given priority in actual development.

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