Programming Forums - View Single Post - Conversion problem. string type to type int.

grumpy · Dec 8th, 2005, 11:58 PM

I assume you want to convert a string like "42" into the value 42.

In vanilla C, this would be done by;

#include <stdlib.h>

int main()
{
    const char v[] = "42";
    int x;
    x = atoi(v);
}

That is deprecated in C++ (i.e. it is allowed, but discouraged and may be removed from a future C++ standard). The C++ equivalent would be;

(Toggle Plain Text)

#include <string>
#include <cstdlib>

int main()
{
    std::string v("42");
    int x;
    x = std::atoi(v.c_str());
}

If you want to do more complex things then you have a few choices, such as;

sscanf() is a C function that reads data from a C-style string

in C++, look up the ostringstream class. An example of it's usage follows;

(Toggle Plain Text)

#include <string>
#include <sstream>
#include <ostream>

int main()
{
    std::string v("42");
    std::ostringstream str(v);
    int x;
    str >> x;   // will get value 42
}

E&OE: I've written the above examples quickly, so may have introduced minor errors. You can also remove the need for "std::" prefixes by judicious use of "using namespace std;", but I prefer code that is guaranteed not to be ambiguous.

Dec 8th, 2005, 11:58 PM	#2
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,223 Rep Power: 5	I assume you want to convert a string like "42" into the value 42. In vanilla C, this would be done by; (Toggle Plain Text) #include <stdlib.h> int main() { const char v[] = "42"; int x; x = atoi(v); } #include <stdlib.h> int main() { const char v[] = "42"; int x; x = atoi(v); } That is deprecated in C++ (i.e. it is allowed, but discouraged and may be removed from a future C++ standard). The C++ equivalent would be; (Toggle Plain Text) #include <string> #include <cstdlib> int main() { std::string v("42"); int x; x = std::atoi(v.c_str()); } #include <string> #include <cstdlib> int main() { std::string v("42"); int x; x = std::atoi(v.c_str()); } If you want to do more complex things then you have a few choices, such as; sscanf() is a C function that reads data from a C-style string in C++, look up the ostringstream class. An example of it's usage follows; (Toggle Plain Text) #include <string> #include <sstream> #include <ostream> int main() { std::string v("42"); std::ostringstream str(v); int x; str >> x; // will get value 42 } #include <string> #include <sstream> #include <ostream> int main() { std::string v("42"); std::ostringstream str(v); int x; str >> x; // will get value 42 } E&OE: I've written the above examples quickly, so may have introduced minor errors. You can also remove the need for "std::" prefixes by judicious use of "using namespace std;", but I prefer code that is guaranteed not to be ambiguous.