printf(1) printf(1) NAME printf - print formatted output SYNOPSIS printf format [arg . . .] DESCRIPTION The printf command converts, formats, and prints its args under control of the format. It fully supports conversion specifications for strings (%s descriptor); however, the results are undefined for the other conversion specifications supported by printf(3S). format a character string that contains three types of objects: 1) plain characters, which are simply copied to the output stream; 2) conversion specifications, each of which results in fetching zero or more args; and 3) C-language escape sequences, which are translated into the corresponding characters. arg string(s) to be printed under the control of format. The results are undefined if there are insufficient args for the format. If the format is exhausted while args remain, the excess args are simply ignored. Each conversion specification is introduced by the character %. After the %, the following appear in sequence: An optional field, consisting of a decimal digit string followed by a $, specifying the next arg to be converted. If this field is not provided, the arg following the last arg converted is used. An optional decimal digit string specifying a minimum field width. If the converted value has fewer characters than the field width, it is padded on the left (or right, if the left-adjustment flag `-' has been given) to the field width. The padding is with blanks unless the field width digit string starts with a zero, in which case the padding is with zeros. An optional precision that gives the maximum number of characters to be printed from a string in %s conversion. The precision takes the form of a period (.) followed by a decimal digit string; a null digit string is treated as zero (nothing is printed). Padding specified by the precision overrides the padding specified by the field width. That is, if precision is specified, its value is used to control the number of characters printed. A field width or precision or both may be indicated by an asterisk (*) instead of a digit string. In this case, an integer arg supplies the field width or precision. The arg 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 arg (if any) to be converted. A negative field width argument is taken as a `-' (left-adjustment) flag followed by a positive field width. Page 1 printf(1) printf(1) If the precision argument is negative, it is changed to zero (nothing is printed). 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. The conversion characters and their meanings are: %s The arg is taken to be a string and characters from the string are printed until a null character (\0) is encountered or the number of characters indicated by the precision specification is reached. If the precision is missing, it is taken to be infinite, so all characters up to the first null character are printed. A null value for arg yields undefined results. %% Print a %; no argument is converted. EXAMPLES The command printf '%s %s %s\n' Good Morning World results in the output: Good Morning World The following command produces the same output. printf '%2$s %s %1$s\n' World Good Morning Here is an example that prints the first 6 characters of $PATH left- adjusted in a 10-character field: printf 'First 6 chars of %s are %-10.6s.\n' $PATH $PATH If $PATH has the value /usr/bin:/usr/local/bin, then the above command would print the following output: First 6 chars of /usr/bin:/usr/local/bin are /usr/b . SEE ALSO printf(3S) Page 2 printf(3S) printf(3S) NAME printf, fprintf, sprintf - print formatted output SYNOPSIS #include int printf(const char *format, .../* args */); int fprintf(FILE *strm, const char *format, .../* args */); int sprintf(char *s, const char *format, .../* args */); DESCRIPTION printf places output on the standard output stream stdout. fprintf places output on strm. sprintf places output, followed by a null character (\0), in consecutive bytes starting at s. It is the user's responsibility to ensure that enough storage is available. Each function returns the number of characters transmitted (not including the terminating null character in the case of sprintf) or a negative value if an output error was encountered. Each of these functions converts, formats, and prints its args under control of the format. The results are undefined if there are insufficient arguments for the format. If the format is exhausted while arguments remain, the excess arguments are simply ignored. The format is a character string that contains two types of objects defined below: 1. plain characters that are simply copied to the output stream; 2. conversion specifications. All forms of the printf functions allow for the insertion of a language- dependent decimal-point character. The decimal-point character is defined by the program's locale (category LC_NUMERIC). In the "C" locale, or in a locale where the decimal-point character is not defined, the decimal-point character defaults to a period (.). Each conversion specification is introduced by the character %, and takes the following general form and sequence: %[posp$][flags][width][.precision][size]fmt posp$ An optional entry, consisting of one or more decimal digits followed by a $ character, specifying the number of the next arg to access. The first arg (just after format) is numbered 1. If this field is not specified, the arg following the most recently used arg will be used. Page 1 printf(3S) printf(3S) flags Zero or more characters that modify the meaning of the conversion specification. The flag characters and their meanings are: - The result of the conversion will be left-justified within the field. (It will be right-justified if this flag is not specified.) + 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.) space If the first character of a signed conversion is not a sign, or if a signed conversion results in no characters, a space will be prefixed to the result. If the space and + flags both appear, the space flag will be ignored. # The value is to be converted to an alternate form. For an o conversion, it increases the precision (if necessary) to force the first digit of the result to be a zero. For x (or X) conversion, a nonzero result will have 0x (or 0X) prefixed to it. For e, E, f, g, and G conversions, the result will always contain a decimal-point character, even if no digits follow it. (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). For c, d, i, s, and u conversions, the flag has no effect. 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. width An optional entry that consists of either one or more decimal digits, or an asterisk (*), or an asterisk followed by one or more decimal digits and a $. It specifies the minimum field width: If the converted value has fewer characters than the field width, it will be padded (with space by default) on the left or right (see the above flags description) to the field width. .prec An optional entry that consists of a period (.) followed by either zero or more decimal digits, or an asterisk (*), or an asterisk followed by one or more decimal digits and a $. It specifies the minimum number of digits to appear for the d, i, o, u, x, and X conversions, the number of digits to appear after the decimal-point 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 characters to be written from a string for an s Page 2 printf(3S) printf(3S) conversion. For other conversions, the behavior is undefined. If only a period is specified, the precision is taken as zero. size An optional h, l (ell), ll (ell ell), or L that specifies other than the default argument type of int for d and i; unsigned int for o, u, x, and X; pointer to int for n; and double for e, E, f, g, and G. If a size appears other than in the following combinations, the behavior is undefined. h For n, the argument has type pointer to short int; for d and i, short int; and for o, u, x, and X, unsigned short int. (For d, i, o, u, x, and X, the argument will have been promoted according to the integral promotions, and its value will be narrowed to short or unsigned short before printing.) l For n, the argument has type pointer to long int; for d and i, long int; and for o, u, x, and X, unsigned long int. ll For n, the argument has type pointer to long long int; for d and i, long long int; and for o, u, x, and X, unsigned long long int. L This flag has no effect in this implementation. fmt A conversion character (described below) that indicates the type of conversion to be applied. When a width or .prec includes an asterisk (*), an int arg supplies the width or precision. When they do not include a $, the arguments specifying a field width, or precision, or both must appear (in that order) before the argument (if any) to be converted. If the conversion specification includes posp$, the field width and precision may include a $. The decimal digits that precede the $ similarly specify the number of the arg that contains the field width or precision. (In this case, posp$ specifies the number of the arg to convert.) A negative field width argument is taken as a - flag followed by a positive field width. If the precision argument is negative, it will be taken as zero. When numbered argument specifications are used, specifying the Nth argument requires that all the leading arguments, from the first to the (N-1)th, be specified at least once, in a consistent manner, in the format string. The conversion characters and their meanings are: d, i The integer arg is converted to signed decimal. 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 a zero value with a precision of zero is no characters. Page 3 printf(3S) printf(3S) o, u, x, X The unsigned integer arg is converted to unsigned octal (o), unsigned decimal (u), or unsigned hexadecimal notation (x and X). The x conversion uses the letters abcdef and the X conversion uses the letters ABCDEF. 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 a zero value with a precision of zero is no characters. f The floating arg is converted to decimal notation in the style [-]ddd.ddd, where the number of digits after the decimal-point character [see setlocale(3C)] is equal to the precision specification. If the precision is missing, it is taken as 6; if the precision is zero and the # flag is not specified, no decimal-point character appears. If a decimal-point character appears, at least one digit appears before it. The value is rounded to the appropriate number of digits. e, E The floating arg is converted to the style [-]d.ddde_dd, where there is one digit before the decimal-point character (which is nonzero if the argument is nonzero) and the number of digits after it is equal to the precision. If the precision is missing, it is taken as 6; if the precision is zero and the # flag is not specified, no decimal-point character appears. The value is rounded to the appropriate number of digits. The E conversion character will produce a number with E instead of e introducing the exponent. The exponent always contains at least two digits. If the value is zero, the exponent is zero. g, G The floating arg is converted 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 decimal-point character appears only if it is followed by a digit. c The integer arg is converted to an unsigned char, and the resulting character is written. C arg is interpreted as a wchar_t, converted to a multi-byte sequence, and the resulting byte(s) are written. s The arg is taken to be a pointer to an array of characters. Characters from the array are written up to (but not including) a terminating null character; if a precision is specified, no more than that many characters are written. If a precision is not specified or is greater than the size of the array, the Page 4 printf(3S) printf(3S) array must contain a terminating null character. (A null pointer for arg will yield undefined results.) S The arg is taken to be a pointer to an array of wide characters (wchar_t). Each character from the array is converted to a multi-byte sequence and the resulting byte(s) are written. Conversion stops when there is a null wide character in the array. If a precision is specified, no more than that many characters are written. If a precision is not specified or is greater than the size of the array, the array must contain a terminating null character. (A null pointer for arg will yield undefined results.) p The arg is taken to be a pointer to void. The value of the pointer is converted to an implementation-defined sequence of printable characters, which matches those read by the %p conversion of the scanf function. n The arg is taken to be a pointer to an integer into which is written the number of characters written so far by this call to printf, fprintf, or sprintf. No argument is converted. % Print a %; no argument is converted. The complete specification must be simply %%. If the form of the conversion specification does not match any of the above, the results of the conversion are undefined. Similarly, 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. If a floating-point value is the internal representation for infinity, the output is [_]inf, where inf is either inf or INF, depending on whether the conversion character is lowercase or uppercase. 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 [_]nan0xm. Depending on the conversion character, nan is either nan or NAN. Additionally, 0xm represents the most significant part of the mantissa. Again depending on the conversion character, x will be x or X, and m will use the letters abcdef or ABCDEF. Printing of the sign follows the rules described above. In no case does a nonexistent or small field width cause truncation of a field; if the result of a conversion is wider than the field width, the field is expanded to contain the conversion result. Characters generated by printf and fprintf are printed as if the putc routine had been called repeatedly. EXAMPLES To print a date and time in the form ``Sunday, July 3, 10:02,'' where weekday and month are pointers to null-terminated strings: Page 5 printf(3S) printf(3S) printf("%s, %s %i, %d:%.2d", weekday, month, day, hour, min); To print pi to 5 decimal places: printf("pi = %.5f", 4 * atan(1.0)); The following two calls to printf both produce the same result of 10 10 00300 10: printf("%d %1$d %.*d %1$d", 10, 5, 300); printf("%d %1$d %3$.*2$d %1$d", 10, 5, 300); SEE ALSO exit(2), lseek(2), write(2), abort(3C), ecvt(3C), setlocale(3C), putc(3S), scanf(3S), stdio(3S). DIAGNOSTICS printf, fprintf, and sprintf return the number of characters transmitted (not counting the terminating null character for sprintf), or return a negative value if an error was encountered. Page 6