Question

I have the following structure and function that adds things to the structure:

struct scoreentry_node {
    struct scoreentry_node *next;
    int score;
    char* name;    
}
;

typedef struct scoreentry_node *score_entry;

score_entry add(int in, char* n, score_entry en) {      
   score_entry r = malloc(sizeof(struct scoreentry_node));
   r->score = in;
   r->name = n;
   r->next = en;  
   return r;   
}

i have input that take it in the following main file:

int score;
char name[];

int main(void) {
score_entry readin = NULL;

while(1)
{

        scanf("%s%d", name, &score);
        readin = add(score, name, readin);
       // blah blah

I dont know why but when input a name it gets added to readin, but when i input another name all the names in readin have this new name

for example:

input:
bob 10 
readin = 10 bob NULL

jill 20
readin = 20 jill 10 jill NULL

I dont know why bob disappears… any reason why it does that ?

Answer 1

You’re just storing a pointer to the name string, not a copy of the string itself. Try using strdup:

r->name = strdup(n);

Just be sure to free(r->name) when freeing a node.

An alternative would be to change char* name to char name[1], and do something like this:

score_entry add(int in, char* n, score_entry en) {      
   score_entry r = malloc(sizeof(struct scoreentry_node) + strlen(n));
   r->score = in;
   strcpy(r->name, n);

   [..]

This saves allocating a separate chunk of memory for the string, but note that in that case name must be at the end of your structure.