C structures and pointers

Question

This is my struct:

typedef struct Person {

    char* name;
    int age;
    float height;
    float weight;
    char** hobbies;

}person;

I tried to fill the name but it just ain't working.

void main(){

    person Asaf;
    char buffer[50];
    int length;

    puts("Please enter the name of the student");
    gets(buffer);
    length = strlen(buffer);
    Asaf.name = realloc(buffer, length);

}

I just can't figure the problem... I guess it has something to do with the realloc function. please help!! :P

what do you think realloc is doing? – Iłya Bursov Feb 18 '15 at 17:53 — Iłya Bursov, Feb 18 '15 at 17:53

jschultz410 · Accepted Answer · 2015-02-18T18:36:20.707

3

You are trying to realloc (which operates on the heap) an array that is allocated on the stack, which is a no-no. What you want instead is something like:

Asaf.name = strdup(buffer);  /* POSIX: allocates a string copy of buffer on the heap */

Or, more standardly:

Asaf.name = (char*) malloc(strlen(buffer) + 1);  /* TODO: should check allocations for NULL return */
strcpy(Asaf.name, buffer);

Also, you should use fgets() rather than gets(). gets() is inherently dangerous and should never be used because it doesn't do any bounds checking on the array to which it writes.

fgets(buffer, sizeof(buffer), stdin);

edited Feb 18 '15 at 18:36

answered Feb 18 '15 at 17:57

jschultz410

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To get around `strdup()` this would do also: `Asaf.name = malloc(strlen(buffer) + 1); /* +1 for the 0-terminator */` The call to `strcpy()` is however still necessary. – alk Feb 18 '15 at 18:13

score 0 · Answer 2 · edited May 23 '17 at 12:20

This function returns a pointer to the newly allocated memory, or NULL if the request fails.

so as realloc operates on heap here getting pointer to the memory allocation in heap area to a pointer guy sitting in stack can cause some problems buddy. so maybe undefined behavior can be the answer for the output you are getting.

About how using realloc, all the didactic examples include this- Use realloc:
1>Check if it's NULL.In this case use perror and exit the program
2>If it's not NULL use the memory allocated
3>Free the memory when you don't need it anymore.

possible duplicate of:How to use realloc in a function in C

C structures and pointers

2 Answers2