Windows asprintf

Privacy policy. Writes formatted data to a string. For more information, see Format Specification Syntax: printf and wprintf Functions. Let len be the length of the formatted data string, not including the terminating null. The snprintf function truncates the output when len is greater than or equal to count , by placing a null-terminator at buffer[count-1]. The value returned is len , the number of characters that would have been output if count was large enough. The snprintf function returns a negative value if an encoding error occurs.

If buffer is a null pointer and count is zero, len is returned as the count of characters required to format the output, not including the terminating null. If buffer is a null pointer and count is nonzero, or if format is a null pointer, the invalid parameter handler is invoked, as described in Parameter Validation.

It's not a part of stdio library. Read the manual on linux, you should be careful if you want your code to be portable. Add a comment. Active Oldest Votes. Improve this answer. Dietrich Epp Dietrich Epp k 35 35 gold badges silver badges bronze badges. Unless I'm totally mistaken. IInspectable: Technically correct according to the C standard, but not actually necessary on Windows.

Are you sure this is true for all platforms including ARM? VS and VS are still fairly common in the wild. Oh, I see, that makes sense then. Thanks for the follow-up. And yes, even VS is still fairly common, probably more so than or Maxxim Maxxim 1, 17 17 silver badges 17 17 bronze badges.

Header file Presumably named asprintf. Community Bot 1 1 1 silver badge. The defines won't work like this. Not only MSVC, but all compilers will fail to honor those. P k 19 19 gold badges silver badges bronze badges. Andrew Siplas Andrew Siplas 9 9 silver badges 14 14 bronze badges. This function is in glibc libary and not supported by Windows.

As far as I knew, asprintf is similiar to sprintf with buffer allocation in it. For d , i , o , u , x , and X conversions, if a precision is specified, the 0 flag will be ignored. If the 0 and ' flags both appear, the grouping characters are inserted before zero padding. For other conversions, the behavior is undefined. 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.

Specifies that a following d , i , o , u , x , or X conversion specifier applies to a short or unsigned short argument the argument will have been promoted according to the integer promotions, but its value will be converted to short or unsigned short before printing ; or that a following n conversion specifier applies to a pointer to a short argument.

Specifies that a following d , i , o , u , x , or X conversion specifier applies to a long long or unsigned long long argument; or that a following n conversion specifier applies to a pointer to a long long argument.

Specifies that a following a , A , e , E , f , F , g , or G conversion specifier applies to a long double argument.

If a length modifier appears with any conversion specifier other than as specified above, the behavior is undefined. Each conversion specifier results in fetching zero or more arguments. If the format is exhausted while arguments remain, the excess arguments are ignored. 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. The unsigned int argument is converted to unsigned octal format in the style dddd.

The unsigned int argument is converted to unsigned decimal format in the style dddd. The unsigned int argument is converted to unsigned hexadecimal format in the style dddd; the letters abcdef are used.

If the precision is missing it is taken as 6; if the precision is explicitly 0 and the flag is not specified, no radix character appears. If a radix character appears, at least 1 digit appears before it.

The converted value is rounded to fit the specified output format according to the prevailing floating point rounding direction mode. If the conversion is not exact, an inexact exception is raised. When the precision is missing it is taken as 6; if the precision is 0 and the flag is not specified, no radix character appears. The E conversion specifier will produce a number with E instead of e introducing the exponent.

The exponent always contains at least two digits. Printing of the sign follows the rules described above. The double argument is printed in style f or e or in style E in the case of a G conversion specifier , with the precision specifying the number of significant digits.

If an explicit precision is 0, it is taken as 1. 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. The A conversion specifier produces a number with ' X ' and ' P ' instead of ' x ' and ' p '.

The exponent will always contain at least one digit, and only as many more digits as necessary to represent the decimal exponent of 2. If the value is zero, the exponent is zero. The int argument is converted to an unsigned char , and the resulting byte is printed. The argument must be a pointer to an array of char. Bytes from the array are written up to but not including any terminating null byte. Speaking of which, here is the double-pointer version of the same code:.

The double-pointer buffer is declared at Line 5. If you the -Wall switch to build this second example of the code, you may see an uninitialized pointer warning. Ignore it. The warning is legitimate but the fix, which is to initialize the pointer to NULL , may crash the program.