You want to make a function that converts from a type to another. Like from std::string to int, or the other way around. This can be done using std::stringstream and insertion / extraction operators. Just as above, templates will prove of great help: Its usage is not as straightforward as the above explained max template. Normally, you would want to call it like "int value = lexical_cast( myStdString );". There is, however, a problem.

In general, when you want to convert from one type to another, the first class to look at is System.Convert. It has a load of static methods which are likely to help you. If you're converting from a String, you could also check whether the type that you want to convert to has a Parse method or something similar - for instance, I usually use DateTime.ParseExact to convert from a String to a DateTime.

There are several ways. The most straightforward is: String myString = numString.trim(); int i = Integer.parseInt(myString); long l = Long.parseLong(myString) or String myString = numString.trim(); i = Integer.parseInt(myString,myIntRadix); Note 1: There is a gotcha with parseInt - it will throw a NumberFormatException for String values in the range "80000000" to "ffffffff". You might expect it to interpret them as negative, but it does not. The values have to be "-80000000" .

Try any of these: String s = String.valueOf(i); or String s = Integer.toString(i); or String s = Integer.toString(i, radix); or // briefer but may result in extra object allocation. String s = "" + i; Note: There are similar classes for Double, Float, Long, etc.

How to add a float (or "any" type really) to the end of a C++ string? Unlike routines like atoi mentioned in the previous question, there is no direct routine such as itoa available. However, similar to the string I/O routines in the previous question, one can do this: #include <stdio.h> // cstdio in C++ // ..

You use static members of the Convert class found in the System namespace to handle conversions in the .NET framework.

This is something you do a lot in programming and pretty much every language makes it easy to convert between types. You may have already printed integers to the console with COUT or PRINTF, which of course needs to be converted to a string first. Converting numbers to strings is done in a similar way. Boost is a C++ library that can help you with problems like these and many others.

I am including the header file <string>, and I am using the string class, but the code doesn't compile? (namespace resolution, having the std:: topics) How do I use unique() with vectors? (answered only once, but still a good question to have due to people not knowing that it's possible to do)

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Well, printf does it for output, so look at its related function named sprintf that "prints formated output to a string."

It's easy. Use sprintf. For example: char string1[50]; char string2[50]; short int var1; float var2; ... sprintf (string1, "%d", var1); sprintf (string2, "%f", var2);

There are two easy ways to do this: you can use the <cstdio> facilities or the <iostream> library. In general, you should prefer the <iostream> library.

If you are reading a host's address from the command line, you may not know if you have an aaa.bbb.ccc.ddd style address, or a host.domain.com style address. What I do with these, is first try to use it as a aaa.bbb.ccc.ddd type address, and if that fails, then do a name lookup on it. Here is an example: Converts ascii text to in_addr struct. NULL is returned if the address can not be found.

The easiest way is to pick up the source for the 100% pure Java class EasyIn from http://www.afu.com/ (same place as this FAQ) Compile it with your code and use it like this: EasyIn easy = new EasyIn(); int i = easy.readInt(); // gets an int from System.in boolean b = easy.readBoolean(); // gets a boolean from System.in double d = easy.readDouble(); // gets a double from System.in ... etc.

The Convert class has an overload of the static ToString() method that takes two ints and returns a string populated with the number in the specified base. For instance, calling Convert.ToString(128, 2) will return "10000000".

It's never necessary to multiply by sizeof(char), since sizeof(char) is, by definition, exactly 1. (On the other hand, multiplying by sizeof(char) doesn't hurt, and in some circumstances may help by introducing a size_t into the expression; see question 7.15.) See also questions 8.9 and 8.10. I wrote a little wrapper around malloc, but it doesn't work: #include <stdio.h> #include <stdlib.

Some libraries have routines strupr and strlwr or strupper and strlower, but these are not Standard or portable. It's a straightforward exercise to write upper/lower-case functions in terms of the toupper and tolower macros in <ctype.h>; see also question 13.5. (The only tricky part is that the function will either have to modify the string in-place or deal with the problem of returning a new string; see question 7.5a.