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@@ -1,5 +1,5 @@
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/*
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/*
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-package fmt implemented formatted I/O with procedures similar to C's printf and Python's format.
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+package fmt implements formatted I/O with procedures similar to C's printf and Python's format.
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The format 'verbs' are derived from C's but simpler.
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The format 'verbs' are derived from C's but simpler.
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Printing
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Printing
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@@ -33,6 +33,8 @@ Floating-point, complex numbers, and quaternions:
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%E scientific notation, e.g. -1.23456E+78
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%E scientific notation, e.g. -1.23456E+78
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%f decimal point but no exponent, e.g. 123.456
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%f decimal point but no exponent, e.g. 123.456
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%F synonym for %f
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%F synonym for %f
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+ %g synonym for %f with default maximum precision
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+ %G synonym for %g
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%h hexadecimal (lower-case) representation with 0h prefix (0h01234abcd)
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%h hexadecimal (lower-case) representation with 0h prefix (0h01234abcd)
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%H hexadecimal (upper-case) representation with 0H prefix (0h01234ABCD)
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%H hexadecimal (upper-case) representation with 0H prefix (0h01234ABCD)
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%m number of bytes in the best unit of measurement, e.g. 123.45mib
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%m number of bytes in the best unit of measurement, e.g. 123.45mib
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@@ -61,9 +63,9 @@ For compound values, the elements are printed using these rules recursively; lai
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bit sets {key0 = elem0, key1 = elem1, ...}
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bit sets {key0 = elem0, key1 = elem1, ...}
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pointer to above: &{}, &[], &map[]
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pointer to above: &{}, &[], &map[]
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-Width is specified by an optional decimal number immediately preceding the verb.
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+Width is specified by an optional decimal number immediately after the '%'.
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If not present, the width is whatever is necessary to represent the value.
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If not present, the width is whatever is necessary to represent the value.
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-Precision is specified after the (optional) width followed by a period followed by a decimal number.
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+Precision is specified after the (optional) width by a period followed by a decimal number.
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If no period is present, a default precision is used.
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If no period is present, a default precision is used.
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A period with no following number specifies a precision of 0.
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A period with no following number specifies a precision of 0.
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@@ -75,7 +77,7 @@ Examples:
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%8.f width 8, precision 0
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%8.f width 8, precision 0
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Width and precision are measured in units of Unicode code points (runes).
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Width and precision are measured in units of Unicode code points (runes).
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-n.b. C's printf uses units of bytes
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+n.b. C's printf uses units of bytes.
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Other flags:
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Other flags:
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@@ -92,7 +94,7 @@ Other flags:
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0 pad with leading zeros rather than spaces
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0 pad with leading zeros rather than spaces
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-Flags are ignored by verbs that don't expect them
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+Flags are ignored by verbs that don't expect them.
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For each printf-like procedure, there is a print function that takes no
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For each printf-like procedure, there is a print function that takes no
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@@ -105,19 +107,20 @@ Explicit argument indices:
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In printf-like procedures, the default behaviour is for each formatting verb to format successive
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In printf-like procedures, the default behaviour is for each formatting verb to format successive
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arguments passed in the call. However, the notation [n] immediately before the verb indicates that
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arguments passed in the call. However, the notation [n] immediately before the verb indicates that
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the nth zero-index argument is to be formatted instead.
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the nth zero-index argument is to be formatted instead.
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-The same notation before an '*' for a width or precision selecting the argument index holding the value.
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-Python-like syntax with argument indices differs for the selecting the argument index: {N:v}
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+The same notation before an '*' for a width or precision specifier selects the argument index
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+holding the value.
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+Python-like syntax with argument indices differs for selecting the argument index: {n:v}
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Examples:
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Examples:
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- fmt.printf("%[1]d %[0]d\n", 13, 37); // C-like syntax
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- fmt.printf("{1:d} {0:d}\n", 13, 37); // Python-like syntax
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+ fmt.printfln("%[1]d %[0]d", 13, 37) // C-like syntax
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+ fmt.printfln("{1:d} {0:d}", 13, 37) // Python-like syntax
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prints "37 13", whilst:
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prints "37 13", whilst:
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- fmt.printf("%[2]*.[1]*[0]f\n", 17.0, 2, 6); // C-like syntax
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- fmt.printf("%{0:[2]*.[1]*f}\n", 17.0, 2, 6); // Python-like syntax
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-equivalent to:
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- fmt.printf("%6.2f\n", 17.0, 2, 6); // C-like syntax
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- fmt.printf("{:6.2f}\n", 17.0, 2, 6); // Python-like syntax
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-prints "17.00"
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+ fmt.printfln("%*[2].*[1][0]f", 17.0, 2, 6) // C-like syntax
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+ fmt.printfln("{0:*[2].*[1]f}", 17.0, 2, 6) // Python-like syntax
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+is equivalent to:
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+ fmt.printfln("%6.2f", 17.0) // C-like syntax
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+ fmt.printfln("{:6.2f}", 17.0) // Python-like syntax
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+and prints "17.00".
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Format errors:
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Format errors:
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