英文:
How to be sure of writing the whole string to file at once in C++
问题
我想执行一个“进程间通信”，使用文件作为中间媒介。生产者向文件写入消息，消费者读取它。
我的问题是关于生产者。
假设这段代码：
#include <iostream>
#include <fstream>
using namespace std;
int main() {
// 创建并打开一个“中间文件”IPC
ofstream messagefile("filename.txt");
// 向文件写入内容
messagefile << "文件可能有些棘手，希望您一次性读取所有这些字符串\n";
// 关闭文件
messagefile.close();
}
是否存在缓冲区刷新的风险（在任何OS或std lib的级别）将此字符串分成多个部分？我想确保消费者进程一次性读取整个消息。你有什么建议？
我知道消费者可以等待特定字符，比如“\n”，但我的问题是关于生产者。
英文:
I want to do an "inter-process communication" with a file in the middle. producer writes messages to the file and the consumer reads it.
my question is about the producer.
assume this code:
#include <iostream>
#include <fstream>
using namespace std;
int main() {
// Create and open a "file in the middle" IPC
ofstream messagefile("filename.txt");
// Write to the file
messagefile << "Files can be tricky, hope you are reading all of this string at once\n";
// Close the file
MyFile.close();
}
Is there any risk that buffer flush (at any level of OS or std lib) flushes this string in more than one part?
I want to ensure that consumer processes read the whole message in one shot. What do you suggest?
I know the consumer can wait for a specific character like "\n", but my question is about the producer.
答案1
得分: 3
如果您担心由于系统崩溃可能导致信息丢失，我建议您使用ostream::flush以及某种依赖于操作系统的调用，将I/O缓冲区真正刷新到磁盘（比如在Unix系统上的sync()）。
如果您只关心IPC协议（即，您只想避免读取部分消息），使用终止符应该足够了。在某些情况下，使用两个不同的分隔符“标记”（开始和结束）可能会有用。
我假设您一次只有一个活跃的写入者。
英文:
If you're concerned about the possible loss of information because of a system crash, I would suggest you to use ostream::flush plus some kind of operating system dependent call for really flushing the I/O buffers to disk (like sync() on Unix systems).
If you're just concerned about the IPC protocol (that is, you just want to avoid reading partial messages), the use of a terminator should be enough. Two different separate "marks" (beginning and end) may be useful in some situations.
I assume you just have one writer active at a time.
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