GCC 4.7 istream :: tellg（）在到达EOF后返回-1 [英] GCC 4.7 istream::tellg() returns -1 after reaching EOF

问题描述

以下代码适用于gcc 4.4。

但是gcc 4.7会给出断言失败。

The following code works with gcc 4.4.
But gcc 4.7 will give assertion failure.

#include <assert.h>
#include <iostream>
#include <sstream>

using namespace std;

int main()
{

    string input("abcdefg");
    stringstream iss(input);
    ostringstream oss;
    oss << iss.rdbuf();

    assert (!iss.eof());
    (void) iss.peek();
    assert (iss.eof());

    // the following assertion will fail with gcc 4.7
    assert( streamoff(iss.tellg()) ==
            streamoff(input.length()) );

    return 0;
}

在gcc 4.7中，如果istream已经达到EOF，tellg -1。没有pubseekoff（）也没有seekoff（）将被称为
在gcc 4.4它不是一个问题。

In gcc 4.7, if the istream has reached EOF, tellg() will return -1. no pubseekoff() nor seekoff() will be called In gcc 4.4 it is not a problem.

这是应该是行为，gcc 4.4 gcc 4.7？为什么？

Which is the supposed to be behavior, gcc 4.4 or gcc 4.7? Why?

推荐答案

根据C ++ 11第27.7.2.3p40节，

According to C++11 section 27.7.2.3p40,

如果 fail（）！= false ，则返回 pos_type（-1）

因此gcc 4.7对当前版本的C ++有正确的行为（假设 peek / code>在流结束时导致 failbit 被设置，并且在哨兵构建期间，因为 skipws 默认设置）。

So gcc 4.7 has the correct behavior for the current version of C++ (assuming that peek() at end of stream causes failbit to be set, and it does during sentry construction, since skipws is set by default).

看看C ++ 03的写法，它是一样的。 27.6.1.3p37。所以你在gcc 4.4中描述的行为是一个错误。

Looking at the wording of C++03, it is the same. 27.6.1.3p37. So the behavior you describe in gcc 4.4 is a bug.

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