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I need to convert a CString to a double, but the function
swscanf_s only operates on float's.
What should I use to convert to a double?
The difficult we do right away...
...the impossible takes slightly longer.
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You can use the wide char versions of atof()[^] or strtod()[^]. If the string does not begin with the numeric value (spaces are ignored), you must parse the string and pass a pointer to the value's offset.
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Signed integers seem to be a minefield of undefined behaviour lurking around every corner. You can't even add them without potentially blowing up the Death Star, unless you test for potential overflow first.
Should they be avoided? How should this be dealt with? How bad is it to pretend it's not a problem?
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know your data. check bounds.
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And here I've been wrestling with unsigned longs (in C#) for the last few days... 
Consider:
ulong max = 1UL << 63 ;
for ( ulong i = max - 1 ; i < max ; i-- )
How many people will freak out when they see the test in the for statement?
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harold aptroot wrote: You can't even add them without potentially blowing up the Death Star, unless you test for potential overflow first.
I'm interested to learn more about this. Can you provide an example of what you mean?
The difficult we do right away...
...the impossible takes slightly longer.
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Not of Death Stars exploding (sadly?).
But there's a well-known (and infamous) optimization that GCC does where if on some code path a signed integer would overflow, it deduces that therefore that code path must be dead. In practice this often means that overflow tests that are done after the overflow has already occurred (such as maybe you calculate something, then don't use the result if the calculation overflowed) are deleted, so your program looks correct (after all, you tested for overflows, right?) but isn't.
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Same could be said about unsigned integers.
"the debugger doesn't tell me anything because this code compiles just fine" - random QA comment
"Facebook is where you tell lies to your friends. Twitter is where you tell the truth to strangers." - chriselst
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or floats, or doubles or any numeric encoding that has to reside on a computer with finite storage.
it's all about what you need the numbers to do for you.
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Exactly.
Chris Losinger wrote: it's all about what you need the numbers to do for you.
Yes it is.
"the debugger doesn't tell me anything because this code compiles just fine" - random QA comment
"Facebook is where you tell lies to your friends. Twitter is where you tell the truth to strangers." - chriselst
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I was wondering why he singled out signed integers. But now that you point this out, I think I understand what he means.
The difficult we do right away...
...the impossible takes slightly longer.
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Signed integers lead to singed digits. 
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No. Unsigned integers wrap, signed integers cause UB. Wrapping can be "not what you wanted", but it does something perfectly predictable and well-defined.
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harold aptroot wrote: Signed integers seem to be a minefield of undefined behaviour
Since their behaviour is completely defined, I find it hard to understand what you mean.
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It isn't. See for example 3.4.3 of C99[^],
An example of undefined behavior is the behavior on integer overflow This does not apply to unsigned integers, which can't overflow because they wrap.
Taking some other standard doesn't help either, as far as I know that's undefined in all version of C and C++ (but I'd really like to be wrong about that).
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Lots and lots of things in C++ (and C for that matter) can lead to undefined behavior if preconditions are not met. Signed integer arithmetic is just one of many. If you're programming in this language, you should be used to dealing with narrow contracts.
So, no, they shouldn't be avoided. Deal with them depending on the situation, in many cases an assert will suffice. Pretending it's not a problem is fatal.
(and no, gcc isn't the only compiler that assumes that naive signed overflow checks are always false)
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Hi,
i am trying to point my vector iterator to some vector index like this:
std::vector::iterator* it= myVec[i];
But it fails:
no known conversion for argument 1 from ‘Data’ to ‘std::vector::iterator
Please help 
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std::vector<int>::iterator it = myVec.begin() + i;
«_Superman_»
I love work. It gives me something to do between weekends.
Microsoft MVP (Visual C++) (October 2009 - September 2013) Polymorphism in C
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Thank you, but can you explain why my version does not work?
Are the types not compatible? I can access vector elements by dereferencing iterators, does it not work the other way around?
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It doesn't work because it is wrong.
Quote: std::vector::iterator* it= myVec[i];
You are trying to assign a value (not an address) to an iterator.
Please note, even
std::vector<int>::iterator* it= &myVec[i];
Would NOT WORK, because iterators are not exactly pointers.
THESE PEOPLE REALLY BOTHER ME!! How can they know what you should do without knowing what you want done?!?!
-- C++ FQA Lite
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Hi,
I have a char array like that represents a double, e.g "1.0004"
If i use atof to get double then i get the value 1, since my locale is using , as decimal separator.
But when i use istringstream i get the correct value. How is that possible? Does it convert BOTH the . and , to decimal separators?
Regards
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stringstream uses the locale information to do the conversion.
You can use _atof_l to achieve the same result.
«_Superman_»
I love work. It gives me something to do between weekends.
Microsoft MVP (Visual C++) (October 2009 - September 2013) Polymorphism in C
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atof() is part of the standard C library that uses the general 'C' locale by default while stringstream is C++ which uses the current system locale by default. You can use the setlocale()[^] function to change the locale for the standard C library functions (pass an empty string to use the environment's default locale).
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