I try to print a variable of type int64_t
using %lld
format specifier but get the following warning?
Warning: format '%lld' expects type 'long long int', but argument 4 has type 'int64_t'
In my opinion, under linux, the int64_t
is always long long int
, then:
how to fix?
Use PRId64
: (Don't forget to include <inttypes.h>
)
printf("var64 = %" PRId64 "\n", var64);
Use PRIx64
and proper cast if you want to print it as hex.
int64_t
is alwayslong long int
, then why does this warning occur?
C99 onwards ( link to draft , Page 22), C specs suggest the type long long int
should be atleast 64 bits but it may be more also.
— minimum value for an object of type long long int
LLONG_MIN -9223372036854775807 // −(2 63 −1)
— maximum value for an object of type long long int
LLONG_MAX +9223372036854775807 // 2 63 − 1
On some platforms, long long int
might be 128-bit and the print statement invokes UB on such platforms.
So treat this warning as a portability issue warning.
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