Open file with input name

Question

I've got this piece of code in C++ from someone else that I am now working with but I'm not sure why the "std::string()" is been added.

std::ifstream File;
std::stringstream FileName;
FileName << Name; //Name being a string that has been passed as an input to the function.
                 // Eg."MyFile"
newFileName << ".txt"; //"MyFile.txt"

File.open(std::string(FileName.str()).c_str(), std::ios::in | std::ios::binary);

My question is, since str() returns a string, and c_str() gets a string and transforms it into c string, why do we need to put it inside the "string()"? Could it not be writen like:

File.open((FileName.str()).c_str(), std::ios::in | std::ios::binary);

std::string() create another temp string object, which is unnecessary. — YaleCheung
– YaleCheung, Commented Feb 15, 2014 at 12:50

Kiril Kirov · Accepted Answer · 2012-11-01 15:35:47Z

1

Yes, it can be written like this.

Using

std::string(FileName.str())

is absolutely meaningless.

answered Nov 1, 2012 at 15:35

Kiril Kirov

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2 Comments

Mulan Over a year ago

So what I wrote is fine eventhough I don't have "using namespace std;" included in my file, right? Thanks for your quick answer!!

Kiril Kirov Over a year ago

@Mulan - yes, it's fine, because toy don't need to have access to this name in this case, using just .str() is OK.

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