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printf(3) Library Functions Manual printf(3) NAME printf, fprintf, sprintf - Print formatted output LIBRARY Standard C Library (libc.so, libc.a) SYNOPSIS #include <stdio.h> int printf( const char *format [,value]...); int fprintf( FILE *stream, const char *format [,value]...); int sprintf( char *string, const char *format [,value]...); STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: fprintf(), printf(), sprintf(): ISO C, XPG4, XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry standards and associated tags. PARAMETERS Specifies a character string combining literal characters with conver- sion specifications. Specifies the data to be converted according to the format parameter. Points to a FILE structure specifying an open stream to which converted values will be written. Points to a charac- ter array in which the converted values will be stored. DESCRIPTION The printf() function converts, formats, and writes its value parame- ters, under control of the format parameter, to the standard output stream stdout. The fprintf() function converts, formats, and writes its value parame- ters, under control of the format parameter, to the output stream spec- ified by the stream parameter. The sprintf() function converts, formats, and stores its value parame- ters, under control of the format parameter, into consecutive bytes starting at the address specified by the string parameter. The sprintf() function places a null character \0 at the end. You must en- sure that enough storage space is available to contain the formatted string. The format parameter is a character string that contains two types of objects: Literal characters, which are copied to the output stream. Conversion specifications, each of which causes zero or more items to be fetched from the value parameter list. If there are not enough items for format in the value parameter list, the results are unpredictable. If more values remain after the entire format has been processed, they are ignored. Conversion Specifications Each conversion specification in the format parameter has the following syntax: A % (percent sign). The printf() functions can handle a format string that enables the system to process elements of the parameter list in variable order. In such a case, the normal conversion character % (per- cent sign) is replaced by %digit$, where digit is a decimal num- ber in the range from 1 to NL_ARGMAX. Conversion is then applied to the specified argument, rather than to the next unused argu- ment. This feature provides for the definition of format strings in an order appropriate to specific languages. When variable ordering is used, the * (asterisk) specification for field width in precision is replaced by *digit$. If the vari- able ordering feature is used, it must be specified for all con- versions. Zero or more flags that modify the meaning of the conversion specification. The flag characters and their meanings are as follows: Format the integer portion of a decimal conver- sion (%i, %d, %u, %f, %g, %G) with the thousands' grouping char- acter. The thousands' grouping character used in the result is the one specified by the current locale for numeric values rather than the one specified for monetary values. The result of using the ' flag with conversions other than decimal is unde- fined. Left align within the field the result of the conver- sion. If you do not specify this flag, the converted value is right aligned within the field. Begin the result of a signed conversion with a sign (+ or -). If you do not specify this flag, the converted value begins with a sign only when the value is negative. Prefix a space character to the result if the first character of a signed conversion is not a sign or if a signed conversion results in no characters. If both the (space) and + flags appear, the (space) flag is ignored. Convert the value to an alternative form. For o conversion, the function increases the precision to force the first digit of the result to be a 0 (zero). For x and X conversions, a nonzero result has 0x or 0X prefixed to it. For e, E, f, g, and G conversions, the result always contains a radix character, even if no digits fol- low it. For g and G conversions, trailing zeros are not removed from the result. For c, C, d, i, s, S, and u conversions, the flag has no effect. Pad to field width using leading zeros (following any indication of sign or base) for d, i, o, u, x, X, e, E, f, g, and G conversions; no space padding is performed. If the 0 and - (dash) flags both appear, the 0 flag is ignored. For d, i, o u, x, and X conversions, if a precision is speci- fied, the 0 flag is also ignored. For other conversions, the behavior is undefined. An optional decimal digit string that specifies the minimum field width. If the converted value has fewer characters than the field width, the field is padded on the left to the length specified by the field width. If the left-adjustment flag is specified, the field is padded on the right. A field width can be indicated by an * (asterisk) instead of a digit string. In this case, an integer (int) value parameter supplies the field width. The value parameter converted for output is not fetched until the conversion letter is reached, so the parameters specifying field width or precision must appear before the value (if any) to be converted. If the corresponding parameter has a negative value, it is treated as a - left align- ment option followed by a positive field width. When variable ordering with the %digit$ format is used, the * (asterisk) spec- ification for field width in precision is replaced by *digit$. An optional precision. The precision is a . (dot) followed by a decimal digit string. If no precision is given, the decimal digit string is treated as 0 (zero). The precision specifies: The minimum number of digits to appear for the d, u, o, x, or X conversions. The number of digits to appear after the radix character for the e, E, and f conversions. The maximum number of significant digits for the g and G conversions. The maximum number of bytes to be printed from a string in the s or the S conversion. A field precision can be indicated by an * (asterisk) instead of a digit string. In this case, an integer (int) value parameter supplies the field precision. The value parameter converted for output is not fetched until the conversion letter is reached, so the parameters specifying field width or precision must appear before the value (if any) to be converted. If the value of the corresponding parameter is negative, the value is treated as if the precision had not been specified. When variable ordering with the %digit$ format is used, the * (asterisk) specification for field width in precision is replaced by *digit$. An op- tional h or l indicating the size of the argument corresponding to the following integer or floating-point conversion specifier. An h followed by a d, i, o, u, x, or X conversion specifier in- dicates that the argument will be treated as a short int or un- signed short int. An h followed by a n indicates that the argu- ment will be treated as a pointer to a short int. An l followed by a d, i, o, u, x, or X conversion specifier indicates that the argument will be treated as a long int or unsigned long int. An l followed by a n indicates that the argument will be treated as a pointer to a long int. [ISO C] An l followed by a c conversion specifier applies to a wint_t argument. An l followed by an s conversion specifier ap- plies to a pointer to a wchar_t argument. One of the following characters to indicate the type of conversion to be applied: Ac- cepts an integer (int) value and converts it to signed decimal notation. The precision specifies the minimum number of digits to appear. If the value being converted can be represented in fewer digits, it is expanded with leading zeros. The default precision is 1. The result of converting a 0 (zero) value with a precision of 0 (zero) is a null string. Specifying a field width with a 0 (zero) as a leading character causes the field width value to be padded with leading zeros. Accepts an integer (int) value and converts it to unsigned decimal notation. The preci- sion specifies the minimum number of digits to appear. If the value being converted can be represented in fewer digits, it is expanded with leading zeros. The default precision is 1. The re- sult of converting a 0 (zero) value with a precision of 0 (zero) is a null string. Specifying a field width with a 0 (zero) as a leading character causes the field width value to be padded with leading zeros. Accepts an integer (int) value and converts it to unsigned octal notation. The precision specifies the minimum number of digits to appear. If the value being converted can be represented in fewer digits, it is expanded with leading zeros. The default precision is 1. The result of converting a 0 (zero) value with a precision of 0 (zero) is a null string. Specifying a field width with a 0 (zero) as a leading character causes the field width value to be padded with leading zeros. An octal value for field width is not implied. Accepts an integer (int) value and converts it to unsigned hexadecimal notation. The let- ters abcdef are used for the x conversion and the letters ABCDEF are used for the X conversion. The precision specifies the mini- mum number digits to appear. If the value being converted can be represented in fewer digits, it is expanded with leading zeros. The default precision is 1. The result of converting a 0 (zero) value with a precision of 0 (zero) is a null string. Specifying a field width with a 0 (zero) as a leading character causes the field width value to be padded with leading zeros. Accepts a float or double value and converts it to decimal notation in the format [-]ddd.ddd. The number of digits after the radix charac- ter is equal to the precision specification. If no precision is specified, six digits are output. If the precision is 0 (zero), no radix character appears (unless the # flag is specified). If a radix character is output, at least one digit is output before it. The value is rounded to the appropriate number of digits. Accepts a float or double value and converts it to the exponen- tial form [-]d.ddde+/-dd. There is one digit before the radix character and the number of digits after the radix character is equal to the precision specification. If no precision is speci- fied, six digits are output. If the precision is 0 (zero), no radix character appears (unless the # flag is specified). The E conversion character produces a number with E instead of e be- fore the exponent. The exponent always contains at least two digits. If the value is 0 (zero), the exponent is 0 (zero). Accepts a float or double value and converts it in the style of the e, E, or f conversion characters, with the precision speci- fying the number of significant digits. If an explicit preci- sion is zero, it is ignored (treated as 1). Trailing zeros are removed from the result. A radix character appears only if it is followed by a digit (except that the radix character always ap- pears if the # flag is specified). The style used depends on the value converted. Style e (E, if G is the flag used) results only if the exponent resulting from the conversion is less than -4, or if the exponent is greater or equal to the precision. If the l qualifier is not present, accepts and prints an integer (int) value converted to an unsigned char. [ISO C] If the l qualifier is present, treats the c argument as wint_t, converts it to a two-element wchar_t array, (the first element being the wint_t argument and the second being a null wide character), and prints the converted value. Accepts a wchar_t value, converts it to an array of bytes containing a multibyte character, and prints the character. If a minimum field width is specified and the multibyte character occupies fewer bytes than the specified width, the multibyte character is padded with space characters to the specified width. If the l qualifier is not present, accepts a pointer to an array of char type. Bytes from the array are printed until a null character is encountered or the number of characters indicated by the preci- sion is reached. If no precision is specified, all characters up to the first null character are printed. If the precision is not specified or is greater than the size of the array, then the array must be terminated by a null byte. If the string pointer value has a value of 0 (zero) or null, the results are unde- fined. [ISO C] If the l qualifier is present, the s argument is treated as a pointer to an array of type wchar_t. Wide charac- ters from the array are converted to multibyte characters. Con- version of each wide-character is done as if by a call to the wcrtomb() function (with the conversion state described by an mbstate_t object initialized to zero before the first wide char- acter is converted) up to (but not including) the terminating null wide character. The resulting bytes (including shift se- quences) are written up to (but not including) the terminating null byte. If no precision is specified, the wide-character ar- ray contains a null wide character. If, for a specified preci- sion, the function would need to access one wide character past the end of the array to equal the length of a complete multi- byte-character sequence, the array also contains a null wide character; in other words, the function does not output a par- tial multibyte character. Accepts a pointer to an array of wchar_t type. Wide characters from the array are converted to an array of bytes containing multibyte characters and the multi- byte characters up to (but not including) the null character are printed. If a precision is specified, then no more than the number of bytes specified by the precision are printed. If the precision is not specified or is greater than the size of the array of bytes, then the array of wide characters must be termi- nated by a null wide character. If a minimum field width is specified and the array of bytes occupy fewer bytes than the specified width, the array is padded with space characters to the specified width. Accepts a pointer to void. The value of the pointer is converted to a sequence of printable characters, the same as unsigned long hexadecimal (lx). Accepts a pointer to an integer into which is written the number of characters written to the output stream so far by this call. No argument is converted. Prints a % wide character. No argument is converted. The complete conversion specification is %%. If a conversion specification is invalid, results are undefined. If any argument is, or points to, a union or an aggregate (except for an array of char type using %s conversion, an array of wchar_t using %s conversion, or a pointer using %p conversion), the function's behavior is undefined. If the result of a conversion is wider than the field width, the field is expanded to contain the converted result. No truncation occurs. However, a small precision can cause truncation on the right. The e, E, f, and g formats represent the special floating-point values as follows: +NaNQ or -NaNQ +NaNS or -NaNS +INF or -INF +0 or -0 The representation of the + (plus sign) depends on whether the + or (space) formatting flag is specified. All forms of the printf() functions allow for the insertion of a lan- guage-dependent radix character in the output string. The radix char- acter is defined by langinfo data in the program's locale (category LC_NUMERIC). In the POSIX (C) locale, or in a locale where the radix character is not defined, the radix character defaults to . (period). The st_ctime and st_mtime fields of the file are marked for update be- tween the successful execution of the printf() or fprintf() function and the next successful completion of a call to one of the following: The fflush() or fclose() function on the same stream The exit() or abort() function RESTRICTIONS Currently, the DIGITAL UNIX product does not include locales that use shift-state encoding. Some sections of this reference page refer to the mb_state object or describe behavior that is dependent on shift- state encoding. This information is included for your convenience in developing portable applications that run on multiple platforms, some of which may supply locales that do use shift-state encoding. RETURN VALUES Upon successful completion, each of these functions returns the number of bytes in the output string. Otherwise, a negative value is re- turned. The value returned by the sprintf() function does not include the final '\0' (null) character. ERRORS The printf() or fprintf() functions fail if either stream is unbuffered or stream's buffer needed to be flushed and the function call caused an underlying write() or lseek() function to be invoked. In addition, if the printf() or fprintf() function fails, errno is set to one of the following values: The O_NONBLOCK flag is set for the file descriptor underlying stream and the process would be delayed in the write opera- tion. The file descriptor underlying stream is not a valid file de- scriptor open for writing. An attempt was made to write to a file that exceeds the process's file size limit or the maximum file size. An in- valid wide character was detected. The read operation was interrupted by a signal that was caught, and no data was transferred. The imple- mentation supports job control; the process is a member of a background process group and is attempting to write to its controlling terminal; TOSTOP is set; the process is neither ignoring nor blocking SIGTTOU; and the process group of the process is orphaned. This error may also be returned under implementation-defined conditions. There was no free space remaining on the device containing the file. An attempt was made to write to a pipe or FIFO that is not open for reading by any process. A SIGPIPE signal will also be sent to the process. RELATED INFORMATION Functions: conv(3), ecvt(3), putc(3), scanf(3), vprintf(3), vw- printf(3), wprintf(3), wscanf(3) delim off printf(3)