How to printf a 64-bit integer as hex

Question

With the following code I am trying to output the value of a unit64 t variable using printf    Compiling the code with gcc  returns the following warning      warning  format     x    expects argument of type    unsigned int       but argument 2 has type    uint64 t     -Wformat     The code    include  lt stdio h gt   include  lt stdint h gt   int main          uint64 t val   0x1234567890abcdef      printf  val   0x x n   val        return 0      The output   val   0x90abcdef   Expected output   val   0x1234567890abcdef   How can I output a 64bit value as a hexadecimal integer using printf    The x specifier seems to be wrong in this case

User · Accepted Answer

The warning from your compiler is telling you that your format specifier doesn't match the data type you're passing to it.

Try using %lx or %llx. For more portability, include inttypes.h and use the PRIx64 macro.

For example: printf("val = 0x%" PRIx64 "\n", val); (note that it's string concatenation)

User · Answer

Edit  Use printf  val   0x   PRIx64   n   val   instead   Try printf  val   0x llx n   val    See the printf manpage       ll  ell-ell   A following integer conversion corresponds to a long long int or unsigned long long int argument  or a following n conversion corresponds to a pointer to a long long int argument     Edit  Even better is what  M Oehm wrote  There is a specific macro for that  because unit64 t is not always a unsigned long long  PRIx64 see also this stackoverflow answer

[c] How to printf a 64-bit integer as hex?

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