#include <stdio.h>
#include <stdlib.h>

int main(int argc, char* argv[]) {
    
    int num_chars = 5;
    char* s = malloc(sizeof(*s) * num_chars);
    // sizeof(*s) gives you the number of bytes per char
    // num_chars is the number of chars (elements) in the new array.
    // This will be on the HEAP (segment of memory).
    
    s[0] = 'Y';
    s[1] = 'o';
    s[2] = 'p';
    s[3] = 'e';
    s[4] = 'e';
    s[5] = 'e';
    s[6] = '\0';

    // BAD
    // char* s = (char*) malloc(sizeof(*s) * num_chars);  // no unnecessary cast
    // char* s = malloc(sizeof(char) * num_chars);        // use sizeof(expr)

    // Note:  sizeof(..) does not access or evaluate the expression so there
    //        is no problem using it before it is initialized.

    printf("%s\n", s);

    free(s);   // VERY IMPORTANT  -- WARNING:  -40% if you forget
    // Forgetting to call free(..) on *each* allocated block is a MEMORY LEAK.
    

    return EXIT_SUCCESS;
}
/*
==34726== Invalid write of size 1
==34726==    at 0x400658: main (malloc_buffer_overflow.c:17)
==34726==  Address 0x4c3e045 is 0 bytes after a block of size 5 alloc'd
==34726==    at 0x4A06A2E: malloc (vg_replace_malloc.c:270)
==34726==    by 0x400618: main (malloc_buffer_overflow.c:7)
==34726==
==34726== Invalid write of size 1
==34726==    at 0x400663: main (malloc_buffer_overflow.c:18)
==34726==  Address 0x4c3e046 is 1 bytes after a block of size 5 alloc'd
==34726==    at 0x4A06A2E: malloc (vg_replace_malloc.c:270)
==34726==    by 0x400618: main (malloc_buffer_overflow.c:7)
==34726==
==34726== Invalid read of size 1
==34726==    at 0x4A07FC4: __GI_strlen (mc_replace_strmem.c:404)
==34726==    by 0x3F1EA6884A: puts (ioputs.c:37)
==34726==    by 0x400671: main (malloc_buffer_overflow.c:27)
==34726==  Address 0x4c3e045 is 0 bytes after a block of size 5 alloc'd
==34726==    at 0x4A06A2E: malloc (vg_replace_malloc.c:270)
==34726==    by 0x400618: main (malloc_buffer_overflow.c:7)
==34726==
==34726== Invalid read of size 1
==34726==    at 0x3F1EA7449E: _IO_default_xsputn (genops.c:485)
==34726==    by 0x3F1EA71601: _IO_file_xsputn@@GLIBC_2.2.5 (fileops.c:1372)
==34726==    by 0x3F1EA688DC: puts (ioputs.c:43)
==34726==    by 0x400671: main (malloc_buffer_overflow.c:27)
==34726==  Address 0x4c3e045 is 0 bytes after a block of size 5 alloc'd
==34726==    at 0x4A06A2E: malloc (vg_replace_malloc.c:270)
==34726==    by 0x400618: main (malloc_buffer_overflow.c:7)
==34726==
Yopeee
==34726==
==34726== HEAP SUMMARY:
==34726==     in use at exit: 0 bytes in 0 blocks
==34726==   total heap usage: 1 allocs, 1 frees, 5 bytes allocated
==34726==
==34726== All heap blocks were freed -- no leaks are possibleO

*** NOTE:  "0 bytes after a block of size 5" means the byte immediately
           following that block.
*/
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