this=0x0 on the debugger

I'm trying to implement a memory manager that manages a block of memory that I allocated using the chained lists to preserve its state but I have some problems

#0 0x6fce11f4   libstdc++-6!_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEC1Ev() (C:\Program Files\CodeBlocks\MinGW\bin\libstdc++-6.dll:??)
#1 0x401bac Programme::Programme(this=0x0) (C:\Users\hoste\Documents\Code Block\Gestionnaire_Memoire\Memoire.cpp:24)
#2 0x401f06 Memoire::ajoutProgramme(this=0x63fdbc, position=0, P=..., L=..., prog=0xca3d08) (C:\Users\hoste\Documents\Code Block\Gestionnaire_Memoire\Memoire.cpp:60)
#3 0x401712 main() (C:\Users\hoste\Documents\Code Block\Gestionnaire_Memoire\main.cpp:23)

Allocation of memory constructor of class programme

function whose call is problematic Calling of the function

debugging the program allows me to see that the P pointer is worth 0x0, but I don't know how to fix it