calloc與malloc的區別

都是動態分配內存。
Both the malloc() and the calloc() functions are used to allocate dynamic memory. Each operates slightly different from the other. malloc() takes a size and returns a pointer to a chunk of memory at least that big:

void *malloc( size_t size ); //分配的大小

calloc() takes a number of elements, and the size of each, and returns a pointer to a chunk of memory
at least big enough to hold them all:

void *calloc( size_t numElements, size_t sizeOfElement ); // 分配元素的個數和每一個元素的大小

主要的不一樣是malloc不初始化分配的內存，calloc初始化已分配的內存爲0。
There are one major difference and one minor difference between the two functions. The major difference is that malloc() doesnt initialize the allocated memory. The first time malloc() gives you a particular chunk of memory, the memory might be full of zeros. If memory has been allocated, freed, and reallocated, it probably has whatever junk was left in it. That means, unfortunately, that a program might run in simple cases (when memory is never reallocated) but break when used harder (and when memory is reused). calloc() fills the allocated memory with all zero bits. That means that anything there you are going to use as a char or an int of any length, signed or unsigned, is guaranteed to be zero. Anything you are going to use as a pointer is set to all zero bits.

That is usually a null pointer, but it is not guaranteed.Anything you are going to use as a float or double is set to all zero bits; that is a floating-point zero on some types of machines, but not on all.

次要的不一樣是calloc返回的是一個數組，而malloc返回的是一個對象。
The minor difference between the two is that calloc() returns an array of objects; malloc() returns one object. Some people use calloc() to make clear that they want an array.

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我的評註：

顯然calloc的效率要比malloc低，若是沒有初始爲0的要求就用malloc。

這裏是「 calloc函數的效率（calloc與malloc+memset效率的對比）」