C11 _Generic c program and errors on Eclipse c/c++ - c

Question

Hi i was studying C for the first time using C primer plus book then in chapter 16 about _Generic from C11 standard i wrote a program in Eclipse c/c++ and build and it produces 8 errors and warning and i don't know why here is the program and the errors
#include <stdio.h>
#include <math.h>
#define RAD_TO_DEG (180/(4 * atanl(1)))
// generic square root function
#define SQRT(X) _Generic((X),\
long double: sqrtl, \
default: sqrt, \
float: sqrtf)(X)
// generic sine function, angle in degrees
#define SIN(X) _Generic((X),\
long double: sinl((X)/RAD_TO_DEG),\
default: sin((X)/RAD_TO_DEG),\
float: sinf((X)/RAD_TO_DEG)\
)
int main(void)
{
float x = 45.0f;
double xx = 45.0;
long double xxx =45.0L;
long double y = SQRT(x);
long double yy= SQRT(xx);
long double yyy = SQRT(xxx);
printf("%.17Lf\n", y); // matches float
printf("%.17Lf\n", yy); // matches default
printf("%.17Lf\n", yyy); // matches long double
int i = 45;
yy = SQRT(i); // matches default
printf("%.17Lf\n", yy);
yyy= SIN(xxx); // matches long double
printf("%.17Lf\n", yyy);
return 0;
}
errors
make all
Building file: ../generic.c
Invoking: GCC C Compiler
gcc -std=c11 -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"generic.d" -MT"generic.d" -o "generic.o" "../generic.c"
../generic.c: In function ‘main’:
../generic.c:24:5: warning: implicit declaration of function ‘_Generic’ [-Wimplicit-function-declaration]
long double y = SQRT(x);
^
../generic.c:7:5: error: expected expression before ‘long’
long double: sqrtl, \
^
../generic.c:24:21: note: in expansion of macro ‘SQRT’
long double y = SQRT(x);
^
../generic.c:7:5: error: expected expression before ‘long’
long double: sqrtl, \
^
../generic.c:25:21: note: in expansion of macro ‘SQRT’
long double yy= SQRT(xx);
^
../generic.c:7:5: error: expected expression before ‘long’
long double: sqrtl, \
^
../generic.c:26:23: note: in expansion of macro ‘SQRT’
long double yyy = SQRT(xxx);
^
../generic.c:7:5: error: expected expression before ‘long’
long double: sqrtl, \
^
../generic.c:31:10: note: in expansion of macro ‘SQRT’
yy = SQRT(i); // matches default
^
../generic.c:13:1: error: expected expression before ‘long’
long double: sinl((X)/RAD_TO_DEG),\
^
../generic.c:33:10: note: in expansion of macro ‘SIN’
yyy= SIN(xxx); // matches long double
^
make: *** [generic.o] Error 1
14:47:53 Build Finished (took 66ms)
i have used -lm link for math.h and it produces these errors and i don't know why ?

Answer 1

Reason:
_Generic is not supported in gcc until version 4.9, see: https://gcc.gnu.org/wiki/C11Status
Solution:
Try a newer version of gcc.
Example:
In a.c is the code you provided:
[pengyu#GLaDOS tmp]$ gcc a.c -std=c11 -lm -Wall -pedantic
[pengyu#GLaDOS tmp]$ gcc --version | head -n 1
gcc (GCC) 4.9.1 20140903 (prerelease)