Dynamic Memory Allocation - Keep seg faulting - c

Question

I have to dynamically allocate memory using these two functions but I keep getting a segfault. The code takes in strings from a file. I need to dynamically allocate memory for a specific number of monsters using structs, pointers and malloc.
typedef struct monster {
char *name;
char *element;
int population;
} monster;
monster* createMonster(char *name, char *element, int population){
//Copying the data into the monster
monster *temp =(monster*) malloc(sizeof(monster));
strcpy(temp->name, name);
strcpy(temp->element, element);
strcpy(temp->population, population);
return temp;
free(temp);
}
monster** readMonsters(FILE* infile, int *monsterCount){
//getting monster count and creating temp pointers
monster **temp = NULL;
char m_word [8];
fscanf(infile, "%d", monsterCount);
fscanf(infile, "%s", m_word); //reading the word monster to skip it
char* temp_name;
char* temp_element;
int temp_pop;
//allocating memory and creating an array of monster pointers * mcount
temp = (monster**)malloc(*monsterCount * sizeof(monster*));
for(int i = 0; i < monsterCount; i++){
fscanf(infile, "%s",temp_name);
fscanf(infile, "%s",temp_element);
fscanf(infile, "%d",temp_pop);
monster *monster_temp = createMonster(temp_name, temp_element, temp_pop);
temp[i]->name = monster_temp->name;
temp[i]->element = monster_temp->element;
temp[i]->population = monster_temp->population;
}
return temp;
}

Answer 1

You haven't posted the definition of struct monster.
If struct monster contains a lot of char* and you are assigning a char* to it, that char* needs to be allocated somewhere. It doesn't look like temp_name and temp_element have been allocated, which would cause a crash on the scanf.

Answer 2

your code segfault because you write at uninitialized and unallocated pointers
you directly write with strcpy name and element field of your struct but these two field point at unknow location
also, you try strcpy an integer, directly assign it : temp->population = population ;
finally you cannot return temp and free temp, if you return it it will be reused, you must not free it, hopefully the free is never reach as you exit the function one line before :)
for storing your strings into the struct, you have some possibilities
declare them as array of char in your structure : char name[64]
use a buffer in your structure and set the name and element field point on part of it
malloc them with strlen of original strings before the copy
directly point name and element vars of your createMonster function to the pointer, it will use original memory, but it's not suitable here as they come from temporary memory
an example of create monster function using a static common buffer for your strings (untested) :
#define MONSTER_MAX_BF 64
typedef struct monster {
char *name;
char *element;
int population;
char bf[MONSTER_MAX_BF];
} monster;
monster* createMonster(char *name, char *element, int population){
monster *temp =(monster*) malloc(sizeof(monster));
char * lastBf = temp->bf + (MONSTER_MAX_BF - 1); // buffer last char
char *bfp = bf, *p ;
// copy name
temp->name = bfp ;
p = name ;
while( *p && *bfp != lastBf ) *bfp++ = *p++ ;
*bfp++ = 0;
// copy element
temp->element = bfp ;
p = element ;
while( *p && *bfp != lastBf ) *bfp++ = *p++ ;
*bfp = 0;
temp->population = population ;
return temp;
}