http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48956
--- Comment #4 from stevenj at alum dot mit.edu 2011-05-11 20:16:57 UTC --- Created attachment 24230 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24230 patch to add a -Wconversion warning for complex -> real conversions I believe the attached patch (against gcc 4.6.0) implements the feature I requested. It emits a warning for implicit conversions of complex types to real (or integer) types. It also emits a warning for similarly converting complex constants, unless the imaginary part of the constant is zero in which case it is treated as a real (or integer) constant given by the real part. Note that complex->complex conversions are still not checked (e.g. no warning is given in converting a complex double to a complex float, etcetera), but at least I didn't add any regressions in that regard. For example, when compiling the following test file: #include <complex.h> #include <math.h> double foo(double complex z) { complex double zc = 1 + 1i; complex double zc0 = 1 + 0i; float complex zf = z; double x = z; float xf = z; int i = z; double xc = 1 + 1i; double xc0 = 1 + 0i; int ic = 1.1 + 1.1i; int ic0 = 1.1 + 0.0i; return sqrt(z) + csqrt(z); } with "gcc -Wconversion -c", the unpatched gcc gives no warnings whereas the patched gcc emits: complex-Wconversion-tst.c: In function ‘foo’: complex-Wconversion-tst.c:11:6: warning: conversion to ‘double’ from ‘complex double’ may alter its value [-Wconversion] complex-Wconversion-tst.c:12:6: warning: conversion to ‘float’ from ‘complex double’ may alter its value [-Wconversion] complex-Wconversion-tst.c:13:6: warning: conversion to ‘int’ from ‘complex double’ may alter its value [-Wconversion] complex-Wconversion-tst.c:15:6: warning: conversion to ‘double’ alters ‘complex int’ constant value [-Wconversion] complex-Wconversion-tst.c:17:6: warning: conversion to ‘int’ alters ‘complex double’ constant value [-Wconversion] complex-Wconversion-tst.c:18:6: warning: conversion to ‘int’ alters ‘double’ constant value [-Wconversion] complex-Wconversion-tst.c:20:6: warning: conversion to ‘double’ from ‘complex double’ may alter its value [-Wconversion] complex-Wconversion-tst.c:20:21: warning: conversion to ‘double’ from ‘complex double’ may alter its value [-Wconversion] Note that two warnings are emitted for the last line: one for the implicit conversion of z to a real number in sqrt(z), and the other for the implicit conversion of the complex sqrt(z)+csqrt(z) to a real return value of foo(z). Using creal(...) and/or explicit casts silences the warnings. Note also that "double xc0 = 1 + 0i;" correctly yields no warning. As mentioned above, "float complex zf = z;" and similar complex->complex conversions probably should emit a warning, but I have not implemented that. However, that is not a regression. --SGJ
