https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116954
Bug ID: 116954
Summary: -Wsuggest-attribute=format false positive for function
template
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: m.gcc.gnu.org at alias dot viem.se
Target Milestone: ---
When defining a function template that calls a standard printf function there
will a -Wsuggest-attribute=format warning when instantiated.
One can not att attribute to function definition template.
And adding a function declaration template with attribute does not help.
/*
Demonstrate -Wsuggest-attribute=format false positive for function template.
Verified also for x86-64.gcc 13.1, 13.2, 13.3, 14.1, 14.2 on godbolt.org
(2024-10-03).
> g++ --version
g++ (Gentoo 13.3.1_p20240614 p17) 13.3.1 20240614
...
> g++ -Wmissing-format-attribute temp-format.cpp
<source>: In instantiation of 'int fn(char (&)[N], const char*, ...) [with
long unsigned int N = 20]':
<source>:21:12: required from here
<source>:13:27: warning: function 'int fn(char (&)[N], const char*, ...) [with
long unsigned int N = 20]' might be a candidate for 'gnu_printf' format
attribute [-Wsuggest-attribute=format]
13 | int ret = std::vsnprintf(buf, N, fmt, ap);
| ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
*/
#include<cstdarg>
#include<cstdio>
template<std::size_t N>
int fn(char (&buf)[N], const char fmt[], ...)
__attribute__ ((__format__ (__printf__, 2, 3)));
template<std::size_t N> int fn(char (&buf)[N], const char fmt[], ...)
// __attribute__ ((__format__ (__printf__, 2, 3))) // error: attributes are
not allowed on a function-definition
{
va_list ap;
va_start(ap, fmt);
int ret = std::vsnprintf(buf, N, fmt, ap); // warning: function âint fn(char
(&)[N], const char*, ...) [with long unsigned int N = 20]â might be a candidate
for âgnu_printfâ format attribute [-Wsuggest-attribute=format]
va_end(ap);
return ret;
}
int main()
{
char buf[20];
return fn(buf, "%d", 42);
}
