Passing a std::vector constructed from istreambuf_iterator

Question

I have the following code:

std::ifstream ifs(fileName, std::ios_base::in | std::ios_base::binary);
std::vector<char> vecdata(std::istreambuf_iterator<char>(ifs), 
                          std::istreambuf_iterator<char>());
image->setData(std::move(vecdata));

setData is declared as follows:

void Image::setData(std::vector<char> && data);

I have the following error:

reader.cpp:752: error: no matching function for call to

'Image::setData(std::vector (&)(std::istreambuf_iterator >, std::istreambuf_iterator > (*)()))'
image->setData(std::move(vecdata));
                                 ^
candidate is:

image.h:12: void Image::setData(std::vector&&)

I am using gcc 4.91

MCVE with gcc 5.4, same behavior : http://rextester.com/QYA50737

Is this a gcc bug?

Thanks

http://stackoverflow.com/questions/5363748/constructor-not-returning-usable-object — halfelf, Mar 14 '17 at 09:56
I got the idea by searching for most vexing parse. The second parameter can be interpreted as an unnamed pointer to a function returning a istreambuf_iterator. But how can the first parameter be interpreted as a function declaration argument? To me it can only be a rvalue — galinette, Mar 14 '17 at 14:57

score 5 · Accepted Answer · answered Mar 14 '17 at 09:56

5

You got Most Vexing Parse: use {} instead of ():

std::vector<char> vecdata{std::istreambuf_iterator<char>(ifs), 
                          std::istreambuf_iterator<char>()};

answered Mar 14 '17 at 09:56

Jarod42

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isn't `std::istreambuf_iterator(ifs)` a value, i.e. not a type? – PiotrNycz Mar 14 '17 at 10:00
@PiotrNycz no, in OP's code it is a variable called `ifs` with the type `std::istreambuf_iterator`. – mch Mar 14 '17 at 10:03
@mch Not a variable; a parameter. – Angew is no longer proud of SO Mar 14 '17 at 10:20
How can `std::istreambuf_iterator(ifs)` be a parameter declaration?? – galinette Mar 14 '17 at 14:59
@galinette: `int main(int (argc), char**(argv))` is valid. Whereas for extra parents here is not needed, it would be for case like `int (*a)[42]` – Jarod42 Mar 14 '17 at 15:06
How is this not the case all the time? I have zillions of constructor calls which could be parsed as function declarations, but this has never been the case until today. – galinette Mar 15 '17 at 07:03

Passing a std::vector constructed from istreambuf_iterator

1 Answers1