Formatting multiple char* strings to an std::string

Question

I have two char* strings and a char* literal that I need to combine into a single std::string. Below is what I am doing. It works, but I don't like the way it looks (3 lines to accomplish it). I am wondering if there is a better way to do it...

std::string strSource = _szImportDirectory;
strSource += "\\";
strSource += _szImportSourceFile;

Thanks for you help!

Seth Carnegie · Accepted Answer · 2011-08-17 20:17:11Z

8

std::string strSource = std::string(_szImportDirectory) + "\\" + _szImportSourceFile;

Is one obvious way.

Another way is to use std::stringstream:

std::stringstream s;
s << _szImportDirectory << '\\' + _szImportSourceFile;
std::string strSource = s.str()

That's the most flexible and maintainable way to do it but it still requires three lines.

answered Aug 17, 2011 at 20:17

Seth Carnegie

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6 Comments

John Fitzpatrick Over a year ago

Thanks. I think if I had a large number of char*'s to combine (which I often do) then the stringstream solution becomes more efficient. I'm going to go with that one for now. And now that I think about it, with the stringstream I can also incorpate int's and anything else that is sendable to a cout, I would assume. That's definitely what I wanted.

John Fitzpatrick Over a year ago

Seth, not really related to the problem at hand, but if I had a stringstream and wanted to get a char* from it, can I get it directly from the stringstream somehow? Or do I get a std::string and then c_str() it?

Seth Carnegie Over a year ago

@John yeah, you need to call str() to "materialize" the string, then c_str() to get the pointer to it. I would save the string that it returns from str() though if you can use it again, because it's not an inexpensive operation.

Bill Over a year ago

@Seth: You need to save the string from str or the memory pointed to by c_str will be deallocated.

Bill Over a year ago

@Seth: when you do s.str() you get a newly allocated string. If you don't capture it then it deallocates at the end the statement. In char* cptr = s.str().c_str();, the temporary only lasts until ;, so the memory c_str() points to is no longer valid by the time you can use cptr. If you're passing the result to another function, like strcpy or some other function that expects a null-terminated char*, then you're OK as long as it doesn't store the pointer.

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Vitaly S. · Accepted Answer · 2011-08-17 21:08:54Z

2

Something like this?

std::string str = std::string(_szImportDirectory).append("\\").append(_szImportSourceFile);

PS: updated with correct code

edited Aug 17, 2011 at 21:08

answered Aug 17, 2011 at 20:19

Vitaly S.

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8 Comments

Vitaly S. Over a year ago

BTW, looks like Java StringBuffer style :)

John Fitzpatrick Over a year ago

Which is a good thing. Truth be told, I really miss all the Java conveniences when working with strings in C++. (Do downvoted comments affect my reputation?)

John Fitzpatrick Over a year ago

String s = strImportDir + "\\" + strImportFile; s.replace("some Regular Expression", "b"); if (s.match("\$\{hi\}") { /* etc */ }; /* Actually I know I can do this all with std::string, but I'm still learning it all */

John Fitzpatrick Over a year ago

Oh and I forgot my favorite String[] a = s.split(",");

Vitaly S. Over a year ago

John, for regexes you can use std::tr1 extension or boost::regex.

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