Arbitrary-Response Filter Design
For a low-pass filter it is sufficient to specify the band edges, as shown in this example on the mathworks website. From your code I suppose that your band edges are

f=[-1,-0.5,-0.4,0.7,0.8,1]

Note that you wrote -0.7 and -0.8 (i.e., with a negative sign), which I assume is a mistake.

Furthermore, think about the desired phase or group delay response. The phase factor exp(-j*pi*f*N-1/2) does not make much sense, an it is probably not what you mean. If you want a linear phase (with delay $N/2$, where $N$ is the filter order) there is no need to use cfirpm, and you could better use firpm.