C printf(3) for int, long and long long that works every time

Submitted by Alexis Wilke on Sat, 07/09/2011 - 00:32

Of Note: This only applies to C99, not C++.

I learned something quite interesting today and wanted to keep a note of it.

Whenever I use a printf() with a format such as %ld and try to compile my code on "many" different platforms, I often get warnings on another one.

The fact is that an int, a long, a long long, an int32_t, int64_t all use a different combination depending on your platform and whether you're running in 32 or 64 bit.

So, the answer to this problem are the #define found in the inttypes.h header file:

PRId8
PRId16
PRId32
PRId64

These entries are used after the % in the format strings. They are strings themselves, so you put them between your % and the rest of your string such as:

printf("The total of %" PRId64 " dollars is the maximum spent this year.\n");

As you can see, that totally eliminate the guessing game... Will PRId64 be %d, %ld, or %lld? The header defines the correct value for you. (oh! year! don't add the "d" afterward!)

In PRId64, replace the 'd' with 'i', 'o', 'u', 'x', 'X' and you'll get the corresponding effect as expected.

They also include PRI... entries for two special types: uintmax_t and uintptr_t.

And if you are one of those people who like to use scanf(), you have the SCN... entries at your disposal.

Really, to see all the possibilities, check out your inttypes.h. Just in case, I made a copy of my current version here (click on the link below to see the file.)

inttypes.h

Source: inttypes.h under Linux, licensed under the GPL.

/* The ISO C99 standard specifies that these macros must only be
   defined if explicitly requested.  */
#if !defined __cplusplus || defined __STDC_FORMAT_MACROS

# if __WORDSIZE == 64
#  define __PRI64_PREFIX    "l"
#  define __PRIPTR_PREFIX    "l"
# else
#  define __PRI64_PREFIX    "ll"
#  define __PRIPTR_PREFIX
# endif

/* Macros for printing format specifiers.  */

/* Decimal notation.  */
# define PRId8        "d"
# define PRId16        "d"
# define PRId32        "d"
# define PRId64        __PRI64_PREFIX "d"

# define PRIdLEAST8    "d"
# define PRIdLEAST16    "d"
# define PRIdLEAST32    "d"
# define PRIdLEAST64    __PRI64_PREFIX "d"

# define PRIdFAST8    "d"
# define PRIdFAST16    __PRIPTR_PREFIX "d"
# define PRIdFAST32    __PRIPTR_PREFIX "d"
# define PRIdFAST64    __PRI64_PREFIX "d"


# define PRIi8        "i"
# define PRIi16        "i"
# define PRIi32        "i"
# define PRIi64        __PRI64_PREFIX "i"

# define PRIiLEAST8    "i"
# define PRIiLEAST16    "i"
# define PRIiLEAST32    "i"
# define PRIiLEAST64    __PRI64_PREFIX "i"

# define PRIiFAST8    "i"
# define PRIiFAST16    __PRIPTR_PREFIX "i"
# define PRIiFAST32    __PRIPTR_PREFIX "i"
# define PRIiFAST64    __PRI64_PREFIX "i"

/* Octal notation.  */
# define PRIo8        "o"
# define PRIo16        "o"
# define PRIo32        "o"
# define PRIo64        __PRI64_PREFIX "o"

# define PRIoLEAST8    "o"
# define PRIoLEAST16    "o"
# define PRIoLEAST32    "o"
# define PRIoLEAST64    __PRI64_PREFIX "o"

# define PRIoFAST8    "o"
# define PRIoFAST16    __PRIPTR_PREFIX "o"
# define PRIoFAST32    __PRIPTR_PREFIX "o"
# define PRIoFAST64    __PRI64_PREFIX "o"

/* Unsigned integers.  */
# define PRIu8        "u"
# define PRIu16        "u"
# define PRIu32        "u"
# define PRIu64        __PRI64_PREFIX "u"

# define PRIuLEAST8    "u"
# define PRIuLEAST16    "u"
# define PRIuLEAST32    "u"
# define PRIuLEAST64    __PRI64_PREFIX "u"

# define PRIuFAST8    "u"
# define PRIuFAST16    __PRIPTR_PREFIX "u"
# define PRIuFAST32    __PRIPTR_PREFIX "u"
# define PRIuFAST64    __PRI64_PREFIX "u"

/* lowercase hexadecimal notation.  */
# define PRIx8        "x"
# define PRIx16        "x"
# define PRIx32        "x"
# define PRIx64        __PRI64_PREFIX "x"

# define PRIxLEAST8    "x"
# define PRIxLEAST16    "x"
# define PRIxLEAST32    "x"
# define PRIxLEAST64    __PRI64_PREFIX "x"

# define PRIxFAST8    "x"
# define PRIxFAST16    __PRIPTR_PREFIX "x"
# define PRIxFAST32    __PRIPTR_PREFIX "x"
# define PRIxFAST64    __PRI64_PREFIX "x"

/* UPPERCASE hexadecimal notation.  */
# define PRIX8        "X"
# define PRIX16        "X"
# define PRIX32        "X"
# define PRIX64        __PRI64_PREFIX "X"

# define PRIXLEAST8    "X"
# define PRIXLEAST16    "X"
# define PRIXLEAST32    "X"
# define PRIXLEAST64    __PRI64_PREFIX "X"

# define PRIXFAST8    "X"
# define PRIXFAST16    __PRIPTR_PREFIX "X"
# define PRIXFAST32    __PRIPTR_PREFIX "X"
# define PRIXFAST64    __PRI64_PREFIX "X"


/* Macros for printing `intmax_t' and `uintmax_t'.  */
# define PRIdMAX    __PRI64_PREFIX "d"
# define PRIiMAX    __PRI64_PREFIX "i"
# define PRIoMAX    __PRI64_PREFIX "o"
# define PRIuMAX    __PRI64_PREFIX "u"
# define PRIxMAX    __PRI64_PREFIX "x"
# define PRIXMAX    __PRI64_PREFIX "X"


/* Macros for printing `intptr_t' and `uintptr_t'.  */
# define PRIdPTR    __PRIPTR_PREFIX "d"
# define PRIiPTR    __PRIPTR_PREFIX "i"
# define PRIoPTR    __PRIPTR_PREFIX "o"
# define PRIuPTR    __PRIPTR_PREFIX "u"
# define PRIxPTR    __PRIPTR_PREFIX "x"
# define PRIXPTR    __PRIPTR_PREFIX "X"


/* Macros for scanning format specifiers.  */

/* Signed decimal notation.  */
# define SCNd8        "hhd"
# define SCNd16        "hd"
# define SCNd32        "d"
# define SCNd64        __PRI64_PREFIX "d"

# define SCNdLEAST8    "hhd"
# define SCNdLEAST16    "hd"
# define SCNdLEAST32    "d"
# define SCNdLEAST64    __PRI64_PREFIX "d"

# define SCNdFAST8    "hhd"
# define SCNdFAST16    __PRIPTR_PREFIX "d"
# define SCNdFAST32    __PRIPTR_PREFIX "d"
# define SCNdFAST64    __PRI64_PREFIX "d"

/* Signed decimal notation.  */
# define SCNi8        "hhi"
# define SCNi16        "hi"
# define SCNi32        "i"
# define SCNi64        __PRI64_PREFIX "i"

# define SCNiLEAST8    "hhi"
# define SCNiLEAST16    "hi"
# define SCNiLEAST32    "i"
# define SCNiLEAST64    __PRI64_PREFIX "i"

# define SCNiFAST8    "hhi"
# define SCNiFAST16    __PRIPTR_PREFIX "i"
# define SCNiFAST32    __PRIPTR_PREFIX "i"
# define SCNiFAST64    __PRI64_PREFIX "i"

/* Unsigned decimal notation.  */
# define SCNu8        "hhu"
# define SCNu16        "hu"
# define SCNu32        "u"
# define SCNu64        __PRI64_PREFIX "u"

# define SCNuLEAST8    "hhu"
# define SCNuLEAST16    "hu"
# define SCNuLEAST32    "u"
# define SCNuLEAST64    __PRI64_PREFIX "u"

# define SCNuFAST8    "hhu"
# define SCNuFAST16    __PRIPTR_PREFIX "u"
# define SCNuFAST32    __PRIPTR_PREFIX "u"
# define SCNuFAST64    __PRI64_PREFIX "u"

/* Octal notation.  */
# define SCNo8        "hho"
# define SCNo16        "ho"
# define SCNo32        "o"
# define SCNo64        __PRI64_PREFIX "o"

# define SCNoLEAST8    "hho"
# define SCNoLEAST16    "ho"
# define SCNoLEAST32    "o"
# define SCNoLEAST64    __PRI64_PREFIX "o"

# define SCNoFAST8    "hho"
# define SCNoFAST16    __PRIPTR_PREFIX "o"
# define SCNoFAST32    __PRIPTR_PREFIX "o"
# define SCNoFAST64    __PRI64_PREFIX "o"

/* Hexadecimal notation.  */
# define SCNx8        "hhx"
# define SCNx16        "hx"
# define SCNx32        "x"
# define SCNx64        __PRI64_PREFIX "x"

# define SCNxLEAST8    "hhx"
# define SCNxLEAST16    "hx"
# define SCNxLEAST32    "x"
# define SCNxLEAST64    __PRI64_PREFIX "x"

# define SCNxFAST8    "hhx"
# define SCNxFAST16    __PRIPTR_PREFIX "x"
# define SCNxFAST32    __PRIPTR_PREFIX "x"
# define SCNxFAST64    __PRI64_PREFIX "x"


/* Macros for scanning `intmax_t' and `uintmax_t'.  */
# define SCNdMAX    __PRI64_PREFIX "d"
# define SCNiMAX    __PRI64_PREFIX "i"
# define SCNoMAX    __PRI64_PREFIX "o"
# define SCNuMAX    __PRI64_PREFIX "u"
# define SCNxMAX    __PRI64_PREFIX "x"

/* Macros for scaning `intptr_t' and `uintptr_t'.  */
# define SCNdPTR    __PRIPTR_PREFIX "d"
# define SCNiPTR    __PRIPTR_PREFIX "i"
# define SCNoPTR    __PRIPTR_PREFIX "o"
# define SCNuPTR    __PRIPTR_PREFIX "u"
# define SCNxPTR    __PRIPTR_PREFIX "x"

#endif    /* C++ && format macros */

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C printf(3) for int, long and long long that works every time