C++ 写入数据时 std::ofstream 中的错误处理
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Error handling in std::ofstream while writing data
提问by Santosh Sahu
I have a small program where i initialize a string and write to a file stream:
我有一个小程序，我在其中初始化一个字符串并写入文件流：
#include<iostream>
#include<fstream>
using namespace std;
int main()
{
std::ofstream ofs(file.c_str());
string s="Hello how are you";
if(ofs)
ofs<<s;
if(!ofs)
{
cout<<"Writing to file failed"<<endl;
}
return 0;
}
My diskspace is very less, and the statement "ofs<" fails. So I know that this is an error logically.
我的磁盘空间非常少，并且语句“ ofs<”失败。所以我知道这在逻辑上是错误的。
The statement "if(!ofs)"does not encounter the above issue, hence I am unable to know why it failed.
语句“if(!ofs)”没有遇到上述问题，因此我不知道它为什么失败。
Please tell me, by which other options I would be able to know that "ofs<has failed.
请告诉我，我可以通过哪些其他选项知道 “ofs<已失败。
Thanks in advance.
提前致谢。
采纳答案by Santosh Sahu
I found a solution like
我找到了一个解决方案
#include<iostream>
#include<fstream>
using namespace std;
int main()
{
std::ofstream ofs(file.c_str());
string s="Hello how are you";
if(ofs)
ofs<<s;
if(ofs.bad()) //bad() function will check for badbit
{
cout<<"Writing to file failed"<<endl;
}
return 0;
}
You can also refer to the below links hereand thereto check for the correctness.
回答by James Kanze
In principle, if there is a write error, badbitshould be set. The
error will only be set when the stream actually tries to write, however,
so because of buffering, it may be set on a later write than when the error occurs, or even after
close. And the bit is “sticky”, so once set, it will stay
set.
原则上，如果有写错误，badbit应该设置。错误只会在流实际尝试写入时设置，但是，由于缓冲，它可能会在比发生错误时更晚的写入时设置，甚至在关闭后设置。并且该位是“粘性的”，因此一旦设置，它将保持设置。
Given the above, the usual procedure is to just verify the status of the
output after close; when outputting to std::coutor std::cerr, after
the final flush. Something like:
鉴于上述情况，通常的程序是在关闭后验证输出的状态；当输出到std::coutor 时std::cerr，在最后一次刷新之后。就像是：
std::ofstream f(...);
// all sorts of output (usually to the `std::ostream&` in a
// function).
f.close();
if ( ! f ) {
// Error handling. Most important, do _not_ return 0 from
// main, but EXIT_FAILUREl.
}
When outputting to std::cout, replace the f.close()with
std::cout.flush()(and of course, if ( ! std::cout )).
当输出到std::cout，更换f.close()用
std::cout.flush()（当然，if ( ! std::cout )）。
AND: this is standard procedure. A program which has a return code of 0
(or EXIT_SUCCESS) when there is a write error is incorrect.
并且：这是标准程序。EXIT_SUCCESS出现写入错误时返回码为 0（或）的程序是不正确的。
