Synopsis
int printf(const char *format,
           ...);
Description

printf writes to the standard output stream using putchar, under control of the string pointed to by format that specifies how subsequent arguments are converted for output.

If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated but are otherwise ignored.

printf returns the number of characters transmitted, or a negative value if an output or encoding error occurred.

Formatted output control strings

The format is composed of zero or more directives: ordinary characters (not ‘%’, which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments, converting them, if applicable, according to the corresponding conversion specifier, and then writing the result to the output stream.

Each conversion specification is introduced by the character ‘%’. After the ‘%’ the following appear in sequence:

As noted above, a field width, or precision, or both, may be indicated by an asterisk. In this case, an int argument supplies the field width or precision. The arguments specifying field width, or precision, or both, must appear (in that order) before the argument (if any) to be converted. A negative field width argument is taken as a ‘-’ flag followed by a positive field width. A negative precision argument is taken as if the precision were omitted.

Some library variants do not support width and precision specifiers in order to reduce code and data space requirements; please ensure that you have selected the correct library in the Printf Width/Precision Support property of the project if you use these.

Flag characters

The flag characters and their meanings are:

‘-’
The result of the conversion is left-justified within the field. The default, if this flag is not specified, is that the result of the conversion is left-justified within the field.
‘+’
The result of a signed conversion always begins with a plus or minus sign. The default, if this flag is not specified, is that it begins with a sign only when a negative value is converted.
space
If the first character of a signed conversion is not a sign, or if a signed conversion results in no characters, a space is prefixed to the result. If the space and ‘+’ flags both appear, the space flag is ignored.
‘#’
The result is converted to an alternative form. For ‘o’ conversion, it increases the precision, if and only if necessary, to force the first digit of the result to be a zero (if the value and precision are both zero, a single ‘0’ is printed). For ‘x’ or ‘X’ conversion, a nonzero result has ‘0x’ or ‘0X’ prefixed to it. For ‘e’, ‘E’, ‘f’, ‘F’, ‘g’, and ‘G’ conversions, the result of converting a floating-point number always contains a decimal-point character, even if no digits follow it. (Normally, a decimal-point character appears in the result of these conversions only if a digit follows it.) For ‘g’ and ‘F’ conversions, trailing zeros are not removed from the result. As an extension, when used in ‘p’ conversion, the results has ‘#’ prefixed to it. For other conversions, the behavior is undefined.
‘0’
For ‘d’, ‘i’, ‘o’, ‘u’, ‘x’, ‘X’, ‘e’, ‘E’, ‘f’, ‘F’, ‘g’, and ‘G’ conversions, leading zeros (following any indication of sign or base) are used to pad to the field width rather than performing space padding, except when converting an infinity or NaN. If the ‘0’ and ‘-’ flags both appear, the ‘0’ flag is ignored. For ‘d’, ‘i’, ‘o’, ‘u’, ‘x’, and ‘X’ conversions, if a precision is specified, the ‘0’ flag is ignored. For other conversions, the behavior is undefined.
Length modifiers

The length modifiers and their meanings are:

‘hh’
Specifies that a following ‘d’, ‘i’, ‘o’, ‘u’, ‘x’, or ‘X’ conversion specifier applies to a signed char or unsigned char argument (the argument will have been promoted according to the integer promotions, but its value will be converted to signed char or unsigned char before printing); or that a following ‘n’ conversion specifier applies to a pointer to a signed char argument.
‘h’
Specifies that a following ‘d’, ‘i’, ‘o’, ‘u’, ‘x’, or ‘X’ conversion specifier applies to a short int or unsigned short int argument (the argument will have been promoted according to the integer promotions, but its value is converted to short int or unsigned short int before printing); or that a following ‘n’ conversion specifier applies to a pointer to a short int argument.
‘l’
Specifies that a following ‘d’, ‘i’, ‘o’, ‘u’, ‘x’, or ‘X’ conversion specifier applies to a long int or unsigned long int argument; that a following ‘n’ conversion specifier applies to a pointer to a long int argument; or has no effect on a following ‘e’, ‘E’, ‘f’, ‘F’, ‘g’, or ‘G’ conversion specifier. Some library variants do not support the ‘l’ length modifier in order to reduce code and data space requirements; please ensure that you have selected the correct library in the Printf Integer Support property of the project if you use this length modifier.
‘ll’
Specifies that a following ‘d’, ‘i’, ‘o’, ‘u’, ‘x’, or ‘X’ conversion specifier applies to a long long int or unsigned long long int argument; that a following ‘n’ conversion specifier applies to a pointer to a long long int argument. Some library variants do not support the ‘ll’ length modifier in order to reduce code and data space requirements; please ensure that you have selected the correct library in the Printf Integer Support property of the project if you use this length modifier.

If a length modifier appears with any conversion specifier other than as specified above, the behavior is undefined. Note that the C99 length modifiers ‘j’, ‘z’, ‘t’, and ‘L’ are not supported.

Conversion specifiers

The conversion specifiers and their meanings are:

‘d’, ‘i’
The argument is converted to 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 is expanded with leading spaces. The default precision is one. The result of converting a zero value with a precision of zero is no characters.
‘o’, ‘u’, ‘x’, ‘X’
The unsigned argument is converted to unsigned octal for ‘o’, unsigned decimal for ‘u’, or unsigned hexadecimal notation for ‘x’ or ‘X’ in the style dddd the letters ‘abcdef’ are used for ‘x’ conversion and the letters ‘ABCDEF’ for ‘X’ conversion. 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 spaces. The default precision is one. The result of converting a zero value with a precision of zero is no characters.
‘f’, ‘F’
A double argument representing a floating-point number is converted to decimal notation in the style [-]ddd.ddd, where the number of digits after the decimal-point character 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. A double argument representing an infinity is converted to ‘inf’. A double argument representing a NaN is converted to ‘nan’. The ‘F’ conversion specifier produces ‘INF’ or ‘NAN’ instead of ‘inf’ or ‘nan’, respectively. Some library variants do not support the ‘f’ and ‘F’ conversion specifiers in order to reduce code and data space requirements; please ensure that you have selected the correct library in the Printf Floating Point Support property of the project if you use these conversion specifiers.
‘e’, ‘E’
A double argument representing a floating-point number is converted in the style [-]d.ddde±dd, where there is one digit (which is nonzero if the argument is nonzero) before the decimal-point character 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 specifier produces a number with ‘E’ instead of ‘e’ introducing the exponent. The exponent always contains at least two digits, and only as many more digits as necessary to represent the exponent. If the value is zero, the exponent is zero. A double argument representing an infinity is converted to ‘inf’. A double argument representing a NaN is converted to ‘nan’. The ‘E’ conversion specifier produces ‘INF’ or ‘NAN’ instead of ‘inf’ or ‘nan’, respectively. Some library variants do not support the ‘f’ and ‘F’ conversion specifiers in order to reduce code and data space requirements; please ensure that you have selected the correct library in the Printf Floating Point Support} property of the project if you use these conversion specifiers.
‘g’, ‘G’
A double argument representing a floating-point number is converted in style ‘f’ or ‘e’ (or in style ‘F’ or ‘e’ in the case of a ‘G’ conversion specifier), 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’) is used only if the exponent resulting from such a conversion is less than -4 or greater than or equal to the precision. Trailing zeros are removed from the fractional portion of the result unless the ‘#’ flag is specified; a decimal-point character appears only if it is followed by a digit. A double argument representing an infinity is converted to ‘inf’. A double argument representing a NaN is converted to ‘nan’. The ‘G’ conversion specifier produces ‘INF’ or ‘NAN’ instead of ‘inf’ or ‘nan’, respectively. Some library variants do not support the ‘f’ and ‘F’ conversion specifiers in order to reduce code and data space requirements; please ensure that you have selected the correct library in the Printf Floating Point Support property of the project if you use these conversion specifiers.
‘c’
The argument is converted to an unsigned char, and the resulting character is written.
‘s’
The argument is be a pointer to the initial element of an array of character type. Characters from the array are written up to (but not including) the terminating null character. If the precision is specified, no more than that many characters are written. If the precision is not specified or is greater than the size of the array, the array must contain a null character.
‘p’
The argument is a pointer to void. The value of the pointer is converted in the same format as the ‘x’ conversion specifier with a fixed precision of 2*sizeof(void *).
‘n’
The argument is a pointer to a signed integer into which is written the number of characters written to the output stream so far by the call to the formatting function. No argument is converted, but one is consumed. If the conversion specification includes any flags, a field width, or a precision, the behavior is undefined.
‘%’
A ‘%’ character is written. No argument is converted.

Note that the C99 width modifier ‘l’ used in conjunction with the ‘c’ and ‘s’ conversion specifiers is not supported and nor are the conversion specifiers ‘a’ and ‘A’.