I found on textbook the following comment about ideal gas specific heat.
The definition of ideal gas specfic heat: $$c=\frac{1}{n} \frac{dQ}{dT}$$ makes sense only if the heat exchanged by the gas can be written ad the variation of a state function that is only a function of temperature.
Indeed for an ideal gas, one defines $c_v$ (at constant $V$) and $c_p$ (at constant $p$), where, rispectively, in isochoric and isobaric process we have $Q=\Delta U(T)$ or $Q=\Delta H(T)$ so
$$c_v=\frac{1}{n} \frac{dU(T)}{dT} \,\,\,\, \mathrm{and} \,\,\,\,\, c_p=\frac{1}{n} \frac{dH(T)}{dT} $$
Nevertheless I do not get the theoretical reason why it would not make sense to define $c$ even when $Q$ is not a state function of temperature only. What are the reasons for saying that?