National Instruments 320682C

Chapter 2 Formatting and I/O Library

Scanning Functions—Format String

Consider the following scanning function:

n = Scan(source, formatstring, targetptr1, ..., targetptrn);

where formatstring contains the information to transform the source argument to the

targetptr arguments.

Format strings for the scanning functions are of the following form.

"source_spec > target_specs_and_literals"

where source_spec is a format specifier that describes the nature of the source parameter and

target_specs_and_literals is a sequence of format specifiers and literal characters that

indicate how to divide and reformat the source argument into the desired target.

Examples of format strings for the scanning functions are:

"%s > %i" "%s > %20f[w10x]"

The character > is a visual reminder of the direction of the data transformation, and also

separates the single source format specifier from the (possibly multiple) target format specifiers

and literals. The source format specifier can be omitted, in which case a %s string format is

assumed. If the source format specifier is omitted, the > character can be omitted also, or

retained for clarity.

Notice that the source format specifier is located to the left of the > symbol, just as the source

parameter is located to the left of the format string. Likewise, the target format specifiers are

located to the right of the > symbol, just as the target parameters are located to the right of the

format string.

Format specifiers describe the inputs and outputs of data transformations. Each format specifier

is of the following form.

% [ rep ] formatcode [[ modifiers ]]

The character % introduces all format specifiers. rep indicates how many times the format

repeats with respect to the arguments. formatcode is a code character which indicates the

nature of the data items being formatted. modifiers is an optional bracket enclosed sequence

of codes which further describe the data format.

The following are examples of format specifiers.

%s[t59] %100i[z] %f

Note: rep is not allowed when formatcode is s or l (string).