Variable Format Strings

   

Format Strings

 

Note : For Date Format String see this topic : DateTime Format Strings

 

Format strings specify required formats to general-purpose formatting routines. Format strings passed to the string formatting routines contain two types of objects--literal characters and format specifiers. Literal characters are copied word for word to the resulting string. Format specifiers fetch arguments from the argument list and apply the formatting to them.

Format specifiers have the following form:

"%" [index ":"] ["-"] [width] ["." prec] type

 

A format specifier begins with a % character. After the percent sign come the following elements, in this order:

 

1.An optional argument zero-offset index specifier (that is, the first item has index 0), [index ":"].
2.An optional left justification indicator, ["-"].
3.An optional width specifier, [width].
4.An optional precision specifier, ["." prec].
5.The conversion type character, type.

 

The following table summarizes the possible values for type.

 

Value

Meaning

d

Decimal. The argument must be an integer value. The value is converted to a string of decimal digits. If the format string contains a precision specifier, it indicates that the resulting string must contain at least the specified number of digits; if the value has less digits, the resulting string is left-padded with zeros.

u

Unsigned decimal. Similar to "d", but no sign is output.

e

Scientific. The argument must be a floating-point value. The value is converted to a string of the form "-d.ddd...E+ddd". The resulting string starts with a minus sign if the number is negative. One digit always precedes the decimal point. The total number of digits in the resulting string (including the one before the decimal point) is given by the precision specifier in the format string; a default precision of 15 is assumed if no precision specifier is present. The "E" exponent character in the resulting string is always followed by a plus or minus sign and at least three digits.

f

Fixed. The argument must be a floating-point value. The value is converted to a string of the form "-ddd.ddd...". The resulting string starts with a minus sign if the number is negative. The number of digits after the decimal point is given by the precision specifier in the format string—a default of 2 decimal digits is assumed if no precision specifier is present.

g

General. The argument must be a floating-point value. The value is converted to the shortest possible decimal string using fixed or scientific format. The number of significant digits in the resulting string is given by the precision specifier in the format string; a default precision of 15 is assumed if no precision specifier is present. Trailing zeros are removed from the resulting string, and a decimal point appears only if necessary. The resulting string uses the fixed-point format if the number of digits to the left of the decimal point in the value is less than or equal to the specified precision, and if the value is greater than or equal to 0.00001. Otherwise the resulting string uses scientific format.

n

Number. The argument must be a floating-point value. The value is converted to a string of the form "-d,ddd,ddd.ddd...". The "n" format corresponds to the "f" format, except that the resulting string contains thousand separators.

s

String. The argument must be a string value. The string or character is inserted in place of the format specifier. The precision specifier, if present in the format string, specifies the maximum length of the resulting string. If the argument is a string that is longer than this maximum, the string is truncated.

x

Hexadecimal. The argument must be an integer value. The value is converted to a string of hexadecimal digits. If the format string contains a precision specifier, it indicates that the resulting string must contain at least the specified number of digits; if the value has fewer digits, the resulting string is left-padded with zeros.

 
Conversion characters may be specified in uppercase as well as in lowercase; both produce the same results.

 

For all floating-point formats, the actual characters used as decimal and thousand separators are obtained from the DecimalSeparator and ThousandSeparator which is set for the user at the operating system level.

 

Index, width, and precision specifiers can be specified directly, using a decimal digit string (for example "%10d"). Note that width is an integer value, while precision is an unsigned integer value. For example,

 

 

Format ('%8.2f', [123.456]);

 

A width specifier sets the minimum field width for a conversion. If the resulting string is shorter than the minimum field width, it is padded with blanks to increase the field width. The default is to right-justify the result by adding blanks in front of the value, but if the format specifier contains a left-justification indicator (an "-" en dash character preceding the width specifier), the result is left-justified by adding blanks after the value.