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多个进程访问同一个文件(Multiple processes accessing the same file)

 多个进程是否可以同时访问（写入）同一个文件？ 使用下面的代码，它似乎工作，但我有我的怀疑。  
 实例中的用例是每次收到电子邮件时都会调用的可执行文件，并将其输出记录到中央文件中。  
if (freopen(console_logfile, "a+", stdout) == NULL || freopen(error_logfile, "a+", stderr) == NULL) {
    perror("freopen");
}
printf("Hello World!");
 
 这是在CentOS上运行并编译为C. 

Is it alright for multiple processes to access (write) to the same file at the same time? Using the following code, it seems to work, but I have my doubts. 
Use case in the instance is an executable that gets called every time an email is received and logs it's output to a central file. 
if (freopen(console_logfile, "a+", stdout) == NULL || freopen(error_logfile, "a+", stderr) == NULL) {
    perror("freopen");
}
printf("Hello World!");
 
This is running on CentOS and compiled as C.

原文：https://stackoverflow.com/questions/9880771

更新时间：2022-03-28 09:03

最满意答案

 你只需连接字符  
SELECT 'EN' + Cast(id as varchar(10))
FROM yourTable
 
 然后，如果您想进行更新：  
UPDATE yourTable
SET yourfield = 'EN' + Cast(id as varchar(10))
 
 如果您有表格中的国家/地区列表：  
SELECT left(country, 2) + cast(id as varchar(10))
FROM yourTable
 
 要么  
UPDATE yourTable
SET yourfield = left(country, 2) + Cast(id as varchar(10))
 
 请参阅SQL Fiddle with Demo 

You would just concatenate the characters 
SELECT 'EN' + Cast(id as varchar(10))
FROM yourTable
 
Then if you want to do an update: 
UPDATE yourTable
SET yourfield = 'EN' + Cast(id as varchar(10))
 
If you have the list of countries in the table: 
SELECT left(country, 2) + cast(id as varchar(10))
FROM yourTable
 
or 
UPDATE yourTable
SET yourfield = left(country, 2) + Cast(id as varchar(10))
 
See SQL Fiddle with Demo

多个进程访问同一个文件(Multiple processes accessing the same file)

最满意答案

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