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2010-05-25T14:21:17Z

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2010-05-25T10:31:14Z

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==Deal with istream exceptions==

<source lang="cpp">/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <cstdlib>
namespace MyLib {
double readAndProcessSum (std::istream&);
}
int main()
{
using namespace std;
double sum;
try {
sum = MyLib::readAndProcessSum(cin);
}
catch (const ios::failure& error) {
cerr << "I/O exception: " << error.what() << endl;
return EXIT_FAILURE;
}
catch (const exception& error) {
cerr << "standard exception: " << error.what() << endl;
return EXIT_FAILURE;
}
catch (...) {
cerr << "unknown exception" << endl;
return EXIT_FAILURE;
}
// print sum
cout << "sum: " << sum << endl;
}
#include <istream>
namespace MyLib {
double readAndProcessSum (std::istream& strm)
{
using std::ios;
double value, sum;

// save current state of exception flags
ios::iostate oldExceptions = strm.exceptions();

/* let failbit and badbit throw exceptions
* - NOTE: failbit is also set at end-of-file
*/
strm.exceptions (ios::failbit | ios::badbit);

try {
/* while stream is OK
* - read value and add it to sum
*/
sum = 0;
while (strm >> value) {
sum += value;
}
}
catch (...) {
/* if exception not caused by end-of-file
* - restore old state of exception flags
* - rethrow exception
*/
if (!strm.eof()) {
strm.exceptions(oldExceptions); // restore exception flags
throw; // rethrow
}
}

// restore old state of exception flags
strm.exceptions (oldExceptions);

// return sum
return sum;
}
}</source>
<pre class=codeResult>a
I/O exception: basic_ios::clear</pre>

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C++ Tutorial/File Stream/istream exceptions - История изменений

в 14:21, 25 мая 2010

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