To concatenate strings using ostringstream

[amanyasin]

i want to concatenate two strings in a string or using ostringstream. Like this:

string str= "first string";

ostringstream ostr;
ostr<<"It is a"<<str;

or

string str2 = "it is a"+str;

Please share any easy way.
Thanks in advance.

[hanst99]

Sorry, I don't really understand your question... you just listed two ways to concatenate strings... what do you want now?

[moorecm]

The first way works. You just have to use ostr.str() to get the string from the stringstream. I think this is overkill for string concatenation because the string class supports it directly.

string str = "first string";

ostringstream ostr;
ostr << "It is a" << str;

The second way doesn't work (exactly as typed above) because operator+() is being applied to a string literal (pointer) not a std::string object. This is rather interesting and I hope you study the following examples.

// here's the "verbose" solution
string str = "it is a";
string st2 += str;

string st2 = str + "it is a"; // works because there is a str.operator+( const char * ) 

So, this is what you wanted semantically:

string st2 = string("it is a") + str;

[amanyasin]

Actually i tries the first way but it gives an error and i have not tested the second way.

[Duthomhas]

What kind of error(s) are you getting?

[amanyasin]

I tried but unable to get required result

static string logFileLastName="fileLastName";
string outLogFname = "TestLog";

string test = outLogFname+logFileLastName;
string test2 = string("Debug")+logFileLastName;
string test3 = logFileLastName + outLogFname.c_str();

result:

test= TestLog
test2= Debug
test3 = TestLog

so, it is not printing the other part.

And using ostringstream, it gives errors.

static string str = "first string";

ostringstream ostr;
ostr << "It is a" << str;

 \algommpcbar.cpp(49) : error C2143: syntax error : missing ';' before '<<'
\algommpcbar.cpp(49) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
\algommpcbar.cpp(49) : error C2371: 'ostr' : redefinition; different basic types
1>

[Duthomhas]

Have you #included <sstream> ?

If not, post the exact code you use (as in, the entire function).

[moorecm]

The entire file would be even better.