https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88371
Bug ID: 88371
Summary: Gratuitous (?) warning regarding an implicit
conversion in pointer arithmetic
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: eyalroz at technion dot ac.il
Target Milestone: ---
See: https://godbolt.org/z/tYn9SX
for a live example and comparison with clang
Se: https://stackoverflow.com/q/53628998/1593077
for the question motivating this bug report.
-------
Consider the following program:
#include <iostream>
template <typename T>
struct wrapper {
T t;
operator T() const { return t; }
T get() const { return t; }
};
int main() {
int a[10];
int* x { a } ;
wrapper<long int> y1{2};
wrapper<unsigned int> y2{2};
wrapper<long unsigned int> y3{2};
std::cout << (x + y1) << '\n';
std::cout << (x + y2) << '\n';
std::cout << (x + y3) << '\n'; // this triggers a warning
std::cout << (x + y3.get()) << '\n';
}
When compiling it (with g++ 8.2.0) with -std=c++2a -Wsign-conversion we get:
a.cpp: In function ‘int main()’:
a.cpp:20:23: warning: conversion to ‘long int’ from ‘long unsigned int’ may
change the sign of the result [-Wsign-conversion]
std::cout << (x + y3) << '\n'; // this triggers a warning
^~
As far as I can tell, both the third and fourth line should trigger a warning,
or none of them should.
Also, a comment on the Stackoverflow page suggested this clause:
http://eel.is/c++draft/over.match.oper#9
may be relevant here.
