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++ // ..

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.

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

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.

Converting from int to string is a little more complicated than converting a string to int. There are no standard C++ functions for this, but there is a way to do it using standard stringstreams. The class stringstream is declared in header sstream and is used like this: std::stringstream ss; std::string str; ss << 31337; ss >> str;

Sometimes programmers think that the [] in the delete[] p only exists so the compiler will call the appropriate destructors for all elements in the array. Because of this reasoning, they assume that an array of some built-in type such as char or int can be deleted without the []. E.g., they assume the following is valid code: But the above code is wrong, and it can cause a disaster at runtime.

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.

The simplest way is to use the function int std::atoi(const char*) declared in cstdlib. For example, std::atoi("31337") returns 31337. Alternatively, you can use std::strtol() or std::strtoul(). These functions provide more functionality such as the ability to convert hexadecimal or octal number strings, and are also declared in cstdlib.

Converting from int to string is a little more complicated than converting a string to int. There are no standard C++ functions for this, but there is a way to do it using standard stringstreams. The class stringstream is declared in header sstream and is used like this:

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.

The C++ compiler must know that f(int,char,float) is to be called by a C compiler using the extern "C" construct: The extern "C" line tells the compiler that the external information sent to the linker should use C calling conventions and name mangling (e.g., preceded by a single underscore). Since name overloading isn't supported by C, you can't make several overloaded functions simultaneously callable by a C program.

If you have an individual C function that you want to call, and for some reason you don't have or don't want to #include a C header file in which that function is declared, you can declare the individual C function in your C++ code using the extern "C" syntax. Naturally you need to use the full function prototype:

Java.lang.String has certain utilities to convert a string into a byte array and visa versa. A string can be converted correctly and fully into a byte array by using a character encoding such as UTF-8, US-ASCII. All the overloaded String.getBytes() methods will convert a string into a byte array. Some of these methods take an encoding identifier as an argument, while others take no arguments and will use the platform's default encoding to convert the string.

I wrote a little wrapper around malloc, but it doesn't work: #include <stdio.h> #include <stdlib.h> mymalloc(void *retp, size_t size) { retp = malloc(size); if(retp == NULL) { fprintf(stderr, "out of memory\n"); exit(EXIT_FAILURE); } } I'm trying to declare a pointer and allocate some space for it, but it's not working.

The first declares an initialized and modifiable array; the second declares a pointer initialized to a not-necessarily- modifiable constant string.

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)

The Standard says that it returns an int (the number of characters written, just like printf and fprintf). Once upon a time, in some C libraries, sprintf returned the char * value of its first argument, pointing to the completed result (i.e. analogous to strcpy's return value).

Why can't I convert a char * to a const char *&? The most common response/solution we've seen offered with respect to this issue is that the person with this problem should just use a cast. Unfortunately, there is normally no additional explanation of the matter. So, that's not helpful in understanding the matter. Worse, it can even be considered harmful advice. The second most common response is a blunt "because", but that doesn't help any either.

Please see Limitations and Workarounds (PDF file) for more details. You may also want to look at some sample converted projects.

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Private Sub ddlCulture_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ddlCulture.SelectedIndexChanged

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.

No. You cannot use them as Vector deals with objects. Standard data types are not objects. However, you can use wrapper classes to convert standard data types to object so that they can be used with Vector. Vector v = new Vector(); // v.add(10); -- cannot be done v.add ( new Integer(10)); // int 10 is converted to object of type Integer class.

Where can I download a free C++ compiler? Updated! [Recently added the compilers.net site thanks to Dejan Milicic plus added Microsoft's command-line compiler (in 3/06). Click here to go to the next FAQ in the "chain" of recent changes.]