Question

I’m compiling on the command line with avr-gcc

One of the includes I’m using has the following lines:

#ifndef F_CPU
#warning No CPU speed specified - assuming Axon is running at 16MHz
#define F_CPU 16000000
#endif

#if F_CPU != 16000000
#warning "AxonII normally runs at 16MHz but you have defined a different value"
#endif

When I run make I get:

In file included from main.c:7:
../webbotavrclib/sys/axon2.h:86:11: error: operator '!=' has no left operand

Line 86 is #if F_CPU != 16000000 above. I’m not sure why I’m getting the error though.

Answer 1

Such message can be produced, for example, for the following compilation:

$ gcc main.c -DF_CPU=
  main.c:6:11: error: operator '!=' has no left operand

Note that F_CPU is defined, but is not anything for != to use.