I want to activate c99 mode in gcc compiler to i read in other post in this forum that
gcc -std=c99 -o outputfile sourcefile.c
As you are using
make you can set the command line options for gcc using
# sample makefile CC = gcc CFLAGS = -Wall -std=c99 OUTFILE = outputfile OBJS = source.o SRCS = source.c $(OUTFILE): $(OBJS) $(CC) $(CFLAGS) -o $(OUTFILE) $(OBJS) $(OBJS): $(SRCS) $(CC) $(CFLAGS) -c $(SRCS)
Addendum (added late 2016): C99 is getting kind of old by now, people looking at this answer might want to explore C11 instead.