[LLVMbugs] [Bug 19611] New: stringstream operator>>(double&) does not correctly convert "INFINITY" to an infinite value

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Apr 29 17:06:55 PDT 2014


            Bug ID: 19611
           Summary: stringstream operator>>(double&) does not correctly
                    convert "INFINITY" to an infinite value
           Product: libc++
           Version: 3.4
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: greg at gregfiumara.com
                CC: llvmbugs at cs.uiuc.edu, mclow.lists at gmail.com
    Classification: Unclassified

A stringstream containing the string "INFINITY" does not produce an infinite
value when calling 'operator>>(double&).' It instead produces the double 0.

In the latest revision of the C++ standard, section states that the
locale's num_get<> should be used for parsing. Section states that,
in num_get<>'s Stage 3, "For a floating-point value, the function strtold (is
used)." The C11 standard states in section that, "The expected form of
the subject sequence is an optional plus or minus sign, then one of the
following...INF or INFINITY, ignoring case." It follows then that a
stringstream containing "INFINITY" should convert to an infinite value.

Below is a piece of code and resulting output demonstrating that the result of
operator>>() does not result in a value that returns true from isinf(). This
code was compiled and run on OS X 10.9.2, with "Apple LLVM version 5.1
(clang-503.0.40) (based on LLVM 3.4svn)."

#include <cmath>
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <sstream>

    const std::string &str)
    double val1 = std::strtod(str.c_str(), nullptr);
    std::cout << str << " - std::isinf from strtod: " << std::boolalpha <<
        std::isinf(val1) << '\n';

    std::stringstream sstream(str);
    double val2;
    sstream >> val2;
    std::cout << str << " - std::isinf from stringstream: " <<
        std::boolalpha << std::isinf(val2) << '\n';

    std::cout << val1 << " vs " << val2 << '\n';

    std::cout << std::endl;


    return (0);

$ clang++ -Wall -Wextra -std=c++11 inf.cpp -o inf
[gfiumara at vito ~]$ ./inf 
INFINITY - std::isinf from strtod: true
INFINITY - std::isinf from stringstream: false
inf vs 0

+INF - std::isinf from strtod: true
+INF - std::isinf from stringstream: true
inf vs inf

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