Advanced Formatting

So far we have only covered formatting specifiers. Format strings actually follow this format, where between each pair of square brackets is a parameter you have to replace with something.

{[position][specifier]:[fill][alignment][width].[precision]}

Name	Meaning
Position	The index of the argument that should be inserted
Specifier	A type-dependent formatting option
Fill	A single character used for padding
Alignment	One of three characters < ^ or >; these are for left, middle and right alignment
Width	The total width of the field (characters)
Precision	How many decimals a formatted number should have

Position usage.

test "position" {
    var b: [3]u8 = undefined;
    try expect(eql(
        u8,
        try bufPrint(&b, "{0s}{0s}{1s}", .{ "a", "b" }),
        "aab",
    ));
}

Fill, alignment and width being used.

test "fill, alignment, width" {
    var b: [6]u8 = undefined;

    try expect(eql(
        u8,
        try bufPrint(&b, "{s: <5}", .{"hi!"}),
        "hi!  ",
    ));

    try expect(eql(
        u8,
        try bufPrint(&b, "{s:_^6}", .{"hi!"}),
        "_hi!__",
    ));

    try expect(eql(
        u8,
        try bufPrint(&b, "{s:!>4}", .{"hi!"}),
        "!hi!",
    ));
}

Using a specifier with precision.

test "precision" {
    var b: [4]u8 = undefined;
    try expect(eql(
        u8,
        try bufPrint(&b, "{d:.2}", .{3.14159}),
        "3.14",
    ));
}