When I use the C function realloc(p,size) in my project, the code runs well in both the simulator and on an iPhone 5.
However, when the code is running on an iPhone 6 plus, some odd things happen. The contents a points to are changed! What's worse, the output is different every time the function runs!
Here is the test code:
#define LENGTH (16)
- (void)viewDidLoad {
[super viewDidLoad];
char* a = (char*)malloc(LENGTH+1);
a[0] = 33;
a[1] = -14;
a[2] = 76;
a[3] = -128;
a[4] = 25;
a[5] = 49;
a[6] = -45;
a[7] = 56;
a[8] = -36;
a[9] = 56;
a[10] = 125;
a[11] = 44;
a[12] = 26;
a[13] = 79;
a[14] = 29;
a[15] = 66;
//print binary contents pointed by a, print each char in int can also see the differene
[self printInByte:a];
realloc(a, LENGTH);
[self printInByte:a]
free(a);
}
-(void) printInByte: (char*)t{
for(int i = 0;i < LENGTH ;++i){
for(int j = -1;j < 16;(t[i] >> ++j)& 1?printf("1"):printf("0"));
printf(" ");
if (i % 4 == 3) {
printf("\n");
}
}
}
One more thing, when LENGTH is not 16, it runs well with assigning up to a[LENGTH-1]. However, if LENGTH is exactly 16, things go wrong.
Any ideas will be appreciated.
From the realloc man doc:
The realloc() function tries to change the size of the allocation pointed to by ptr to size, and returns ptr. If there is not enough room to enlarge the memory allocation pointed to by ptr, realloc() creates a new allocation, copies as much of the old data pointed to by ptr as will fit to the new allocation, frees the old allocation, and returns a pointer to the allocated memory.
So, you must write: a = realloc(a, LENGTH); because in the case where the already allocated memory block can't be made larger, the zone will be moved to another location, and so, the adress of the zone will change. That is why realloc return a memory pointer.