Printf format codes binary trading
As pointed out in PR1: Elementary string conversions there is a number of use cases that do not require internationalization support, but do require high throughput when produced by a server. The need for locale-independent functions for conversions between integers and strings and between floating-point numbers and strings has also been highlighted in N Therefore a user should be able to easily control whether to use locales or not during formatting.
We follow Python's approach  and designate a separate format specifier 'n' for locale-aware numeric formatting. It applies to all integral and floating-point types. All other specifiers produce output unaffected by locale settings.
This can also have positive effect on performance because locale-independent formatting can be implemented more efficiently. An important feature for localization is the ability to rearrange formatting arguments because the word order may vary in different languages . Unfortunately these positional specifiers are not portable . The formatting library has been designed with performance in mind.
It tries to minimize the number of virtual function calls and dynamic memory allocations done per a formatting operation. In particular, if formatting output can fit into a fixed-size buffer allocated on stack, it should be possible to avoid them altogether by using a suitable API.
To this end, a buffer abstraction represented by the fmt:: A buffer is a contiguous block of memory that can be accessed directly and can optionally grow. Only one virtual function, grow , needs to be called during formatting and only when the buffer is not large enough. The locale-independent formatting can also be implemented more efficiently than the locale-aware one. However, the main goal for the former is to support specific use cases see Locale support rather than to improve performance.
In order to minimize binary code size, each formatting function that uses variadic templates is a small inline wrapper around its non-variadic counterpart. This wrapper creates an object representing an array of argument references with fmt:: For example, the format variadic function calls vformat. Multiple argument type codes can be combined and passed into a formatting function as a single integer if the number of arguments is small. Since argument types are known at compile time this can be an integer constant and there will be no code generated to compute it, only to store according to calling conventions.
Given a reasonable optimizing compiler, this will result in a compact per-call binary code, effectively consisting of placing argument pointers or, possibly, copies for primitive types and packed argument type codes on stack and calling a formatting function. This results in somewhat smaller and faster code because the string size, which is not used, doesn't have to be computed and passed. Also having a termination character makes parsing easier. Anything that is not contained in braces is considered literal text, which is copied unchanged to the output.
A brace character can be included in the literal text by doubling: In less formal terms, the replacement field can start with an arg-id that specifies the argument whose value is to be formatted and inserted into the output instead of the replacement field. The arg-id is optionally followed by a format-spec , which is preceded by a colon ': These specify a non-default format for the replacement value.
If the numerical arg-id s in a format string are 0, 1, 2, The format-spec field contains a specification of how the value should be presented, including such details as field width, alignment, padding, decimal precision and so on. Each value type can define its own formatting mini-language or interpretation of the format-spec. Most built-in types support a common formatting mini-language, which is described in the next section.
A format-spec field can also include nested replacement fields in certain position within it. These nested replacement fields can contain only an argument index; format specifications are not allowed. This allows the formatting of a value to be dynamically specified. Format specifications are used within replacement fields contained within a format string to define how individual values are presented see Format string syntax. Each formattable type may define how the format specification is to be interpreted.
Most built-in types implement the following options for format specifications, although some of the formatting options are only supported by the numeric types. The presence of a fill character is signaled by the character following it, which must be one of the alignment options. If the second character of format-spec is not a valid alignment option, then it is assumed that both the fill character and the alignment option are absent.
The meaning of the various alignment options is as follows:. If there are less, zeros are used to fill the space. Newline, tab, and other special characters. That is, whatever binary you pass binary one, format can pass to the other without change. When printf sees a field specifier, perl substitutes the corresponding value options the printf printf list. This can be useful for displaying ordinal values of characters in arbitrary strings:.
Haris on December 5th, Default argument promotions happen in variadic functions. Then printf is most likely what is needed. See below for more details and see sprintf 3 or printf 3 on your system for an explanation of the general principles.
Subbu on January 18th, You add a constant to a format string! Other mobile website rss feed my photos life in alaska how i sold my business living in talkeetna, printf my bookmarks inspirational quotes perl code snippets. Email The content of binary field is kept private and will not be shown printf.
Each month, over 50 million options come to Stack Overflow to perl, share their knowledge, and build options careers. The default state for streams, as stated by the standard, is: The state of the internal format stream can be changed by manipulators passed along with the argument; via the group function, like that:.
When passing N items inside a 'group' Boost. Such manipulators are passed to the streams right before the following argument, at every occurence. Note that formatting options specified within the format string are overridden by stream state modifiers passed this way. For instance in the following code, the hex manipulator has priority over the d type-specification in the format-string which would set decimal output:.
When format detects that one of these rules is not satisfied, it raises a corresponding exception, so that the mistakes don't go unnoticed and unhandled. But the user can change this behaviour to fit his needs, and select which types of errors may raise exceptions using the following functions:.
The user can compute the argument newexcept by combining the following atoms using binary arithmetic:. For instance, if you don't want Boost. The performance of boost:: The result may greatly depend on the compiler, standard library implementation, and the precise choice of format-string and arguments.
Since common stream implementations eventually call functions of the printf family for the actual formatting of numbers, in general printf will be noticeably faster than the direct stream operations And due to to the reordering overhead allocations to store the pieces of string, stream initialisation at each item formatting,..