std::string teststring="The number is: ";
int test_int=1000;
sprintf(teststring.c_str(),"%d",test_int);
sprintf() equivalent for std::string?
Author
Hello all!
I am currently making a settings configuration program and I want a quick way to be able to print a single std::string representing a display mode. To do this, it would be very helpful to have something similar to sprintf() to quickly add non-string enitities like integers to my display mode string.
I tried the following, and it didn't work (I didn't expect it to.) But it gives you the idea of what I'm trying to do.
Thanks for any help!
-synth_cat
Something like:
int test_int=1000;
std::sstream teststring << "The number is: " << test_int;
// to get the std::string type: teststring.str()
That's why I prefer AnsiString over std::string :)
int test_int=1000;
std::sstream teststring << "The number is: " << test_int;
// to get the std::string type: teststring.str()
That's why I prefer AnsiString over std::string :)
Author
I think I've found out the way you're supposed to do this, using an ostringstream object. This is outlined
here.
However, I don't know how to cast an std::ostringstream to a const char* value so I can use TextOut() to print it. I could do this with an std::string with the c_Str() member function, but std::ostringstream seems to lack this method.
Can anyone help me out?
int anumber = 10;std::stringstream stream;stream << "The number is: " << anumber;const char * cptr = stream.str().c_str();Quote:Original post by cmptrgear
const char * cptr = stream.str().c_str()
This looks dangerous, since stream.str() is very likely to create a temporary std::string instance which will be immediately destructed again, taking the c_str with it. cptr will then point to deallocated memory. Try to consistantly pass around std::strings instead of bare char*s, or be very careful with your object lifetimes :)
hh10k is correct.
It would be quite acceptable to do this:
since you are only using the pointer inside the expression in which the temporary std::string is created. However, if you need to use the text data in subsequent statements, you need to do:
It would be quite acceptable to do this:
ostringstream Os; Os << 23;TextOut(Hw,10,20,Os.str().c_str());since you are only using the pointer inside the expression in which the temporary std::string is created. However, if you need to use the text data in subsequent statements, you need to do:
ostringstream Os; Os << 23;std::string s=Os.str();TextOut(Hw,10,20,s.c_str());SomeOtherFunctionTakingConstCharStar(s.c_str());
Author
Thanks a lot - I understand better now.
But I still have a question about this ostringstream object. This comes from the site where I first found out about ostringstream,
here.
Basically, why is there an std::string in this snippet that is never used? Does std::ostreamstring automatically output to the last std::string created?
Also, is it possible to use the << operator to take an ostreamstring object and write a string to itself like so?
But I still have a question about this ostringstream object. This comes from the site where I first found out about ostringstream,
here.
string str;ostringstream strstrm;strstrm << boolalpha << true << " is a bool value" << noboolalpha << ", so is " << false; cout << strstrm.str() << endl;strstrm.str("");strstrm << "100 decimal = " << dec << 100 << ", octal = " << 100 << ", hex = " << hex << 100 << endl;cout << strstrm.str();strstrm.str("");float f = 199.9273f;strstrm << "A float: " << f << ", scientific notation " << f << " " << scientific << f << " fixed notation " << fixed << f << endl;cout << strstrm.str();strstrm.str("");strstrm << "Formatted to two decimal places " << setprecision(2) << f << ", formatted to %2.5f " << setprecision(5) << leftprec(f, 2) << endl; cout << strstrm.str();Basically, why is there an std::string in this snippet that is never used? Does std::ostreamstring automatically output to the last std::string created?
Also, is it possible to use the << operator to take an ostreamstring object and write a string to itself like so?
std::ostreamstring stream;std::string text = "String Text";stream << "The string says " << text;
Quote:Original post by synth_catThe variable str in the example appears to be extraneous.
But I still have a question about this ostringstream object. This comes from the site where I first found out about ostringstream,
here.
*** Source Snippet Removed ***
Basically, why is there an std::string in this snippet that is never used?
Quote:Also, is it possible to use the << operator to take an ostreamstring object and write a string to itself like so?You're not 'writing the string to itself' (the string and the stringstream are different objects), but yes, you can insert a string into a stringstream just like with any other output stream (ostream, ofstream, etc.).
*** Source Snippet Removed ***
This topic is closed to new replies.
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