This piece of codes works fine even with minGW compiler under C++11 standards:
#include <iostream>
int main(int argc, char const *argv[])
{
printf("haha");
return 0;
}
Why should this work? I didn't include stdio.h but I can use functions like printf() and rand(). Are they included in iostream? At least I didn't find them included. If you say that it's included in iostream, show me the evidence.
It's implementation defined if that works or not.
The implementation may include additional headers it needs, but you as a developer should not rely on that and include cstdio too which is the guaranteed way to get access to std::printf.
Including stdio.h puts printf in the global namespace and that is usually not what one wants in C++, so stick with cstdio.
It appears your implementation puts printf in the global namespace even though you've only included a C++ header. That's unfortunate, but that happens too.
Evidence: My preprocessor is called cpp and I can use it to list the included header files. I have this program that I've called std.cpp:
#include <iostream>
int main() {}
and if I use cpp to list a small subset of the included headers
cpp -M std.cpp | tr -d '\\' | tr ' ' '\n' | \
grep -E '^/[^\.]+$' | awk -F/ '{print $NF}'
I get these C++ headers on my system:
iostream
ostream
ios
iosfwd
cwchar
exception
typeinfo
new
type_traits
cstdint
clocale
cctype
string
initializer_list
cstdlib
cstdio
cerrno
system_error
stdexcept
streambuf
cwctype
istream
and yes, cstdio is in there which also includes stdio.h.
As @Ted Lyngmo stated it's implementation defined, usually <cstdio> is included, as is <cstdlib>.
My <iostream> header file includes:
#include <bits/c++config.h>
Which in term includes:
/* Define if C99 functions or macros in <stdio.h> should be imported in
<cstdio> in namespace std for C++11. */
#define _GLIBCXX11_USE_C99_STDIO 1
And
/* Define if C99 functions or macros in <stdio.h> should be imported in
<cstdio> in namespace std for C++98. */
#define _GLIBCXX98_USE_C99_STDIO 1
The same for <stdlib.h>.
Implementation info:
Thread model: posix
gcc version 9.2.0 (tdm64-1)
You can open the include file and see the following chain of includes: iostream => istream => ostream => ios => xlocknum => cstdio
The cstdio is C++ wrapper of stdio.h
All highlighted names are standard headers, the chain between ios and cstdio is compiler-dependent (in my case xlocknum is internal from VS2017 compiler)
