Using pointer after free()

During my tests, I have found that it is possible to use pointer after free(). I have the following code: ``` typedef struct{ int module_id; int adc_id; struct config_line * pnext; } config_line; config_line * create_list() { config_line * phead = (config_line *) malloc(sizeof(config_line)); phead->pnext=NULL; phead->module_id = 1; phead->adc_id = 2; printf("module_id=%d adc_id=%d\n",phead->module_id, phead->adc_id); free(phead); printf("module_id=%d adc_id=%d\n",phead->module_id, phead->adc_id); phead->module_id = 2; phead->adc_id = 5; printf("module_id=%d adc_id=%d\n",phead->module_id, phead->adc_id); } ``` The output of this code is: ``` module_id=1 adc_id=2 module_id=0 adc_id=2 module_id=2 adc_id=5 ``` Why after free(phead) I can get access (read and write) to pointer? Why there is not segmentation fault?