There is this code:
#include <cstdio>
#include <chrono>
int main()
{
auto d = std::chrono::microseconds(1).count();
printf("%lld", d);
return 0;
}
When this is compiled in 64bit mode, then there is a warning:
main.cpp: In function 'int main()': main.cpp:7:19: warning: format '%lld' expects argument of type 'long long int', but argument 2 has type 'long int' [-Wformat=] printf("%lld", d); ^
This warning is not present when compiling in 32bit mode (with -m32 flag). It looks like that std::chrono::duration::rep
is of type long int
in 64bit programs and long long int
in 32bit programs.
Is there a portable way to print it like %zu
specifier for size_t
?
As you said that the usage of std::cout
is not an option you can cast the value to the smallest needed data type 1 here it's long long int
2 and use the corresponding conversion specifier:
printf("%lld", static_cast<long long int>(d));
To avoid the explicit cast you can also use the data type directly instead of the auto specifier :
long long int d = std::chrono::microseconds(1).count();
printf("%lld", d);
1 With smallest needed data type I mean the smallest type that can represent the value in both implementations.
2 The long long int
type has to be at least 64 bit wide, see here on SO .
I suggest you use std::cout
, since you are in C++. This will be portable.
However, if you must use printf, change this:
printf("%lld", d);
to this:
#include <cinttypes>
printf("%" PRId64 "", d);
Another approach would be to cast d
to the highest data type (which can hold both types), like this:
printf("%lld", static_cast<long long int>(d));
You can cast it to long long int
before printing:
#include <cstdio>
#include <chrono>
int main()
{
auto d = std::chrono::microseconds(1).count();
printf("%lld", static_cast<long long int>(d));
return 0;
}
But it seems me that it is better to use std::cout
Instead of using the auto
qualifier, use a fixed size integer int64_t.
#include <cstdio>
#include <chrono>
#include <cinttypes>
int main()
{
int64_t d = std::chrono::microseconds(1).count();
printf("%" PRId64 "\n", d);
return 0;
}
A portable (ie C++) approach to consider, that does not use std::cout
{
// create a string:
std::ostringstream ss;
ss << d;"
// then
printf("%s", ss.str().c_str());
}
or perhaps
{
printf("%s", std::to_string(d).c_str() );
}
为了避免警告,你可以将d转换为long long int。
printf("%lld", static_cast<long long int> (d));
Perhaps not directly related to the 32/64 bit problem at hand, but some of us are on embedded systems with odd output consoles and C++ libraries. (Plus we know that if we have to do any serious output formatting, printf is saner than iomanip!)
Anyway, this prints the guts of a duration and may be useful for debugging. Modify to taste.
template<typename Rep, typename Ratio>
printf_dur( std::chrono::duration< Rep, Ratio > dur )
{
printf( "%lld ticks of %lld/%lld == %.3fs",
(long long int) dur.count(),
(long long int) Ratio::num,
(long long int) Ratio::den,
( (Ratio::num == 1LL)
? (float) dur.count() / (float) Ratio::den
: (float) dur.count() * (float) Ratio::num
)
);
}
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