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Text File | 2002-01-05 | 17.6 KB | 390 lines

<H3>SYNOPSIS</H3> int printf(const char *format, /* args*/ ...); int sprintf(char *s, const char *format, /* args*/ ...); The printf() function places output on the output stream stdout. The sprintf() function places output, followed by the null byte (\0), in consecutive bytes starting at s; the CScript engine ensures that enough storage is available. Each of these functions converts, formats, and prints its args under control of the format. The format is a character string, beginning and ending in its initial shift state, if any. The format is composed of zero or more directives defined as follows: <UL> <LI>ordinary characters, which are simply copied to the output stream;</LI> <LI>escape sequences, which represent non-graphic characters; and</LI> <LI>conversion specifications, each of which results in the fetching of zero or more arguments.</LI> </UL> The results are undefined if there are insufficient arguments for the format. If the format is exhausted while arguments remain, the excess arguments are evaluated but are otherwise ignored. Conversions can be applied to the nth argument after the format in the argument list, rather than to the next unused argument. In this case, the conversion character % (see below) is replaced by the sequence %n$, where n is a decimal integer in the range [1, NL_ARGMAX], giving the position of the argument in the argument list. This feature provides for the definition of format strings that select arguments in an order appropriate to specific languages (see the EXAMPLES section). In format strings containing the %n$ form of conversion specifications, numbered arguments in the argument list can be referenced from the format string as many times as required. In format strings containing the % form of conversion specifications, each argument in the argument list is used exactly once. Escape Sequences The following escape sequences produce the associated action on display devices capable of the action: <UL> <LI>\n Newline. Move the printing position to the start of the next line.</LI> <LI>\r Carriage return. Move the printing position to the start of the current line.</LI> <LI>\t Horizontal tab. Move the printing position to the next implementation-defined horizontal tab position on the current line.</LI> </UL> Conversion Specifications Each conversion specification is introduced by the character % or by the character sequence %n$, after which the following appear in sequence: <UL> <LI>An optional field, consisting of a decimal digit string followed by a $, specifying the next args to be converted. If this field is not provided, the args following the last args converted will be used.</LI> <LI>Zero or more flags (in any order), which modify the meaning of the conversion specification.</LI> <LI>An optional minimum field width. If the converted value has fewer bytes than the field width, it will be padded with spaces by default on the left; it will be padded on the right, if the left-adjustment flag (-), described below, is given to the field width. The field width takes the form of an asterisk (*), described below, or a decimal integer. If the conversion character is s, a standard-conforming application interprets the field width as the minimum number of bytes to be printed; an application that is not standard-conforming interprets the field width as the minimum number of columns of screen display. For an application that is not standard- conforming, %10s means if the converted value has a screen width of 7 columns, 3 spaces would be padded on the right. If the format is %ws, then the field width should be interpreted as the minimum number of columns of screen display.</LI> <LI>An optional precision that gives the minimum number of digits to appear for the d, i, o, u, x, or X conversions (the field is padded with leading zeros); the number of digits to appear after the radix character for the e, E, and f conversions, the maximum number of significant digits for the g and G conversions; or the maximum number of bytes to be printed from a string in s and S conversions. The precision takes the form of a period (.) followed either by an asterisk (*), described below, or an optional decimal digit string, where a null digit string is treated as 0. If a precision appears with any other conversion character, the behavior is undefined. If the conversion character is s or S, a standard-conforming application interprets the precision as the maximum number of bytes to be written; an application that is not standard-conforming interprets the precision as the maximum number of columns of screen display. For an application that is not standard-conforming, %.5s would print only the portion of the string that would display in 5 screen columns. Only complete characters are written. For %ws, the precision should be interpreted as the maximum number of columns of screen display. The precision takes the form of a period (.) followed by a decimal digit string; a null digit string is treated as zero. Padding specified by the precision overrides the padding specified by the field width.</LI> <LI>An optional h specifies that a following d, i, o, u, x, or X conversion character applies to a type short int or unsigned short int argument (the argument will be promoted according to the integral promotions and its value converted to type short int or unsigned short int before printing); an optional h specifies that a following n conversion character applies to a pointer to a type short int argument. An optional l (ell) specifies that a following d, i, o, u, x, or X conversion character applies to a type long int or unsigned long int argument; an optional l (ell) specifies that a following n conversion character applies to a pointer to a type long int argument. An optional ll (ell ell) specifies that a following d, i, o, u, x, or X conversion character applies to a type long long or unsigned long long argument; an optional ll (ell ell) specifies that a following n conversion character applies to a pointer to a long long argument. An optional L specifies that a following e, E, f, g, or G conversion character applies to a long double argument. If an h, l, or L appears before any other conversion character, the behavior is undefined.</LI> <LI>A conversion character (see below) that indicates the type of conversion to be applied.</LI> </UL> A field width or precision may be indicated by an asterisk (*) instead of a digit string. In this case, an integer args supplies the field width or precision. The args that is actually converted is not fetched until the conversion letter is seen, so the args specifying field width or precision must appear before the args (if any) to be converted. If the precision argument is negative, it will be changed to zero. A negative field width argument is taken as a - flag, followed by a positive field width. A negative precision is taken as if the precision were omitted. In format strings containing the %n$ form of a conversion specification, a field width or precision may be indicated by the sequence *m$, where m is a decimal integer in the range [1, NL_ARGMAX] giving the position in the argument list (after the format argument) of an integer argument containing the field width or precision, for example: <BLOCKQUOTE> <CODE>printf("%1$d:%2$.*3$d:%4$.*3$d\n", hour, min, precision, sec);</CODE> </BLOCKQUOTE> The format can contain either numbered argument specifications (that is, %n$ and *m$), or unnumbered argument specifications (that is, % and *), but normally not both. The only exception to this is that %% can be mixed with the %n$ form. The results of mixing numbered and unnumbered argument specifications in a format string are undefined. When numbered argument specifications are used, specifying the Nth argument requires that all the leading arguments, from the first to the (N-1)th, are specified in the format string. Flag Characters The flag characters and their meanings are: <UL> <LI>' The integer portion of the result of a decimal conversion (%i, %d, %u, %f, %g, or %G) will be formatted with thousands' grouping characters. For other conversions the behavior is undefined. The non-monetary grouping character is used.</LI> <LI>- The result of the conversion will be left-justified within the field. (It will be right-justified if this flag is not specified.) <LI>+ The result of a signed conversion will always begin with a sign (+ or -). (It will begin with a sign only when a negative value is converted if this flag is not specified.)</LI> <LI>space If the first character of a signed conversion is not a sign, a space will be placed before the result. This means that if the space and + flags both appear, the space flag will be ignored. <LI># The value is to be converted to an alternate form. For c, d, i, s, and u conversions, the flag has no effect. For an o conversion, it increases the precision to force the first digit of the result to be a zero. For x (or X) conversion, a non-zero result will have 0x (or 0X) prepended to it. For e, E, f, g, and G conversions, the result will always contain a radix character, even if no digits follow the point (normally, a decimal point appears in the result of these conversions only if a digit follows it). For g and G conversions, trailing zeros will not be removed from the result as they normally are.</LI> <LI>0 For d, i, o, u, x, X, e, E, f, g, and G conversions, leading zeros (following any indication of sign or base) are used to pad to the field width; no space padding is performed. If the 0 and - flags both appear, the 0 flag will be ignored. For d, i, o, u, x, and X conversions, if a precision is specified, the 0 flag will be ignored. For other conversions, the behavior is undefined. </UL> Conversion Characters Each conversion character results in fetching zero or more args. The results are undefined if there are insufficient args for the format. If the format is exhausted while args remain, the excess args are ignored. The conversion characters and their meanings are: <UL> <LI>d,i The int argument is converted to a signed decimal in the style [-]dddd. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it will be expanded with leading zeros. The default precision is 1. The result of converting 0 with an explicit precision of 0 is no characters.</LI> <LI>o The unsigned int argument is converted to unsigned octal format in the style dddd. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it will be expanded with leading zeros. The default precision is 1. The result of converting 0 with an explicit precision of 0 is no characters.</LI> <LI>u The unsigned int argument is converted to unsigned decimal format in the style dddd. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it will be expanded with leading zeros. The default precision is 1. The result of converting 0 with an explicit precision of 0 is no characters.</LI> <LI>x The unsigned int argument is converted to unsigned hexadecimal format in the style dddd; the letters abcdef are used. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it will be expanded with leading zeros. The default precision is 1. The result of converting ing 0 with an explicit precision of 0 is no characters.</LI> <LI>X Behaves the same as the x conversion character except that letters ABCDEF are used instead of abcdef.</LI> <LI>f The double args is converted to decimal notation in the style [-]ddd.ddd, where the number of digits after the radix character is equal to the precision specification. If the precision is omitted from arg, six digits are output; if the precision is explicitly zero and the # flag is not specified, no radix character appears. If a radix character appears, at least 1 digit appears before it. The value is rounded to the appropriate number of digits.</LI> <LI>e,E The double args is converted to the style [-]d.ddde_dd, where there is one digit before the radix character (which is non-zero if the argument is non-zero) and the number of digits after it is equal to the precision. When the precision is missing, six digits are produced; if the precision is zero and the # flag is not specified, no radix character appears. The E conversion character will produce a number with E instead of e introducing the exponent. The exponent always contains at least two digits. The value is rounded to the appropriate number of digits.</LI> <LI>g,G The double args is printed in style f or e (or in style E in the case of a G conversion character), with the precision specifying the number of significant digits. If the precision is zero, it is taken as one. The style used depends on the value converted: style e (or E) will be used only if the exponent resulting from the conversion is less than -4 or greater than or equal to the precision. Trailing zeros are removed from the fractional part of the result. A radix character appears only if it is followed by a digit.</LI> <LI>c The int args is converted to an unsigned char, and the resulting byte is printed.</LI> <LI>s The args is taken to be a string (character pointer) and characters from the string are written up to (but not including) a terminating null byte. If a precision is specified, a standard-conforming application will write only the number of bytes specified by precision; an application that is not standard-conforming will write only the portion of the string that will display in the number of columns of screen display specified by precision. If the precision is not specified, it is taken to be infinite, so all bytes up to the first null byte are printed. A null value for args will yield undefined results.</LI> <LI>% Print a %; no argument is converted. The entire conversion specification must be %%.</LI> </UL> If a conversion specification does not match one of the above forms, the behavior is undefined. If a floating-point value is the internal representation for infinity, the output is [_]Infinity, where Infinity is either Infinity or Inf, depending on the desired output string length. Printing of the sign follows the rules described above. If a floating-point value is the internal representation for "not-a-number," the output is [_]NaN. Printing of the sign follows the rules described above. In no case does a non-existent or small field width cause truncation of a field; if the result of a conversion is wider than the field width, the field is simply expanded to contain the conversion result. Characters generated by printf() are printed as if the function had been called. <H3>RETURN VALUES</H3> The printf() and sprintf() functions return the number of bytes transmitted (not including the \0 in the case of sprintf()). The snprintf() function returns the number of characters formatted, that is, the number of characters that were written to the buffer. Each function returns a negative value if an output error was encountered. <H3>EXAMPLES</H3> Example 1: To print the language-independent date and time format, the following statement could be used: <BLOCKQUOTE> printf (format, weekday, month, day, hour, min); </BLOCKQUOTE> For American usage, format could be a pointer to the string: <BLOCKQUOTE> "%s, %s %d, %d:%.2d\n" </BLOCKQUOTE> producing the message: <BLOCKQUOTE> Sunday, July 3, 10:02 </BLOCKQUOTE> whereas for German usage, format could be a pointer to the string: <BLOCKQUOTE> "%1$s, %3$d. %2$s, %4$d:%5$.2d\n" </BLOCKQUOTE> producing the message: <BLOCKQUOTE> Sonntag, 3. Juli, 10:02 </BLOCKQUOTE> Example 2: To print a date and time in the form Sunday, July 3, 10:02, where weekday and month are pointers to null-terminated strings: <BLOCKQUOTED> printf("%s, %s %i, %d:%.2d", weekday, month, day, hour, min); </BLOCKQUOTED> Example 3: To print pi to 5 decimal places: <BLOCKQUOTED> printf("pi = %.5f", 4 * atan(1.0)); </BLOCKQUOTED>