g++ -Wall not warning about double-> int cast

Question

In the following snippet no warnings are produced. g++4.4.3 -Wall -pedantic

//f is
void f(int );

f(3.14);
double d = 3.14;
int i = d+2;

I

Answer 1

$ gcc -Wconversion test.c

test.c: In function ‘main’:
test.c:3: warning: conversion to ‘int’ from ‘double’ may alter its value

Answer 2

Apart from what other answers mention it is also worth mentioning that in C++0x {} initialization doesn't narrow. So instead of getting a warning you'll get an error for example

void f(int x)
{
   // code
}

int main()
{
   f({3.14}); // narrowing conversion of '3.14000000000000012434497875801753252744674682617e+0' from 'double' to 'int' inside { }
}

g++ 4.4 and above support initializer list (with -std=c++0x option)

Answer 3

Use -Wconversion option. -Wall doesn't include it.

With -Wconversion option, GCC gives these warning messages:

warning: conversion to 'int' alters 'double' constant value
warning: conversion to 'int' from 'double' may alter its value