CODEWITHSUNDEEP
carrays
hidemyname
hidemyname

Reputation: 4287

Why there are some strange numbers in the uninitialized array?

I use two ways to create array. I used to think they are the same but they seem different.

  char *buffer=malloc((sizeof(char)*100));
  char buffer1[100];
  strcpy(buffer,"Eric");
  strcpy(buffer1,"Eric");
for (int i=0; i<100; i++) {
    printf("%c",buffer[i]);
}
  printf("\n");
for (int i=0; i<100; i++) {
    printf("%c",buffer1[i]);
}

the result is 

Eric
Eric?!^?{"Gl?(?!^?(?!^?@?!^?0?P?!^?

And I inspected the array then I found there are some strange numbers in the array. But why when I created the array using malloc. The strange numbers didn't exist?

Upvotes: 0

Views: 81

Answers (1)

Doug Currie
Doug Currie

Reputation: 41180

Apparently, malloc on your system is clearing the returned memory. This may be done to prevent data from leaking from one process to another, or to help with debugging. Or you may have just gotten lucky, and next time malloc won't clear the memory, e.g., because it came from a pool that is already local to your process. So, don't count on it. calloc is available for this purpose.

The second mechanism just adjusts a stack pointer. Whatever was on the stack before the function was entered is still there. Clearing it would cost time, so C compilers do not generate code to do so.

Upvotes: 3

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