String Formatting

For formatting strings there are a couple of different options:

Using ezFormatString as an Argument

ezFormatString is a class that can be easily used as a function parameter to accept formatted strings:

void Print(const ezFormatString& text);

A function that takes just an ezFormatString has to be called with the ezFmt wrapper:

Print(ezFmt("Hello {}", "World"));

The ezFmt function is a variadic template, that can take up to 10 arguments and wraps them all up into an ezFormatString object.

If you want your Print function to be a little bit more convenient, and not require the use of ezFmt, you can add an overload that provides the variadic template functionality directly.

template <typename... ARGS>
void Print(const char* szFormat, ARGS&&... args)
    Print(ezFormatStringImpl<ARGS...>(szFormat, std::forward<ARGS>(args)...));

Now Print can be called like this:

Print("Hello {}", "World");

Inside Print, all you need to do to get the formatted string is to call ezFormatString::GetText():

void Print(const ezFormatString& text)
    ezStringBuilder tmp;
    const char* szResult = text.GetText(tmp);

    // do something with szResult, do not use tmp, as it is not guaranteed to hold the result (meaning, it may not have been needed)

Using ezFormatString

Once a function takes an ezFormatString (see above), you can use {} notation to indicate where an argument shall be inserted.

Positional Arguments

If a formatting string contains {}, every instance will use the next argument, as given to the function. You can also use {n} with n being 0 to 9 to insert the n-th argument. This allows you to skip, rearrange, or repeat arguments:

Print("Arg1: {1}, Arg2: {2}, Arg1: {1}", "zero", "one", "two");

Formatting Options

Most types that can be formatted, can be passed in directly:

Print("int value is {}", 23);

However, often you may want to specify exactly how to display the value. To do so, you need to wrap the incoming argument in an option struct. Each option struct can have arbitrary parameters to configure how it works.

Print("HEX: 0x{}", ezArgU(value, 8, true, 16, true));

ezArgU is an option struct for unsigned int values. Here we specify that the output should have a fixed width of 8 characters, should pad the output with zeros if necessary, use base 16 (hex) and upper case letters.

There are many such option structs available, each with their own parameters. By convention, all formatting option structs are named ezArgXYZ.

Available Option Structs

This is a not necessarily complete list of available option structs:

Custom Argument Formatters

You can easily write your own formatter. The formatting work is done by a free function called BuildString, overloaded for the type that it shall format. If you search for BuildString functions, you will find many overloads, each handling a different type. Please look at those functions to see how to write your own formatter.

For it to work, all that is necessary, is that your code is #include‘d when it is used in a format string. If you try to use a type (such as MyType) in a format string and your custom formatter is not known (#include‘d) in that cpp file, you will get a compile time error with a very long message telling you that no overload of of BuildString is available to handle this type.

The ezArgXYZ structs are just used to wrap a type and store additional options. This is not required, for BuildString to work, but it does allow you to wrap the same type multiple times to select different formatters. For example, unsigned int is wrapped by ezArgU for regular int formatting options, by ezArgFileSize to print a value with B, KB, MB or GB suffixes and by ezArgErrorCode to interpret it as a Windows error code and translate it to a readable string. If you have a custom type MyType and you do not need any formatting options, you can write a BuildString overload, that takes a MyType directly.

See Also