Question

I have a linked list and a setter function.

struct my_struct {
    int    value;
    int  type;
    char   *name;
    struct my_struct *next;
};

struct my_struct *setValue(struct my_struct *s, char *name, int b) {
    if(s!=NULL) {
        while(s != NULL) {
            if( strcmp(s->name,name) == 0) {
                s->value = b;
            }
            s=s->next;
        }
        return s;
    }
    return NULL;
}

Here, name is the search keyword and b is new value of s->value. Why s->value cannot change? After that function, the output is weird. I can’t understand, what happened.

Answer 1

You need to be testing the strings equality with strcmp, as seen below. In your code, you’re testing if two pointers are equal ^{[related post]}.

#include <string.h>

if(strcmp(s->name, name) == 0) { // if both strings are equal
    s->value = b;
}

The location of your return statement is interesting. You’re returning the address of the last item that was changed, which may be undesired.

As per @Matthew Iselin’s comment, change your loop to the following:

while(s != NULL) {
    ...
}

---

In case you are setting the root node to the return value of the function, s will always be NULL after looping through the linked list, therefore the function will always return NULL.