什么是C中的malloc()？ (What is malloc() in C?)

malloc() is a library function that allows C to allocate memory dynamically from the heap. The heap is an area of memory where something is stored.

malloc()是一個庫函數(shù)，它允許C從堆動態(tài)分配內(nèi)存。 堆是存儲內(nèi)容的內(nèi)存區(qū)域。

malloc() is part of stdlib.h and to be able to use it you need to use #include <stdlib.h>.

malloc()是stdlib.h的一部分，要使用它，您需要使用#include <stdlib.h> 。

如何使用Malloc (How to Use Malloc)

malloc() allocates memory of a requested size and returns a pointer to the beginning of the allocated block. To hold this returned pointer, we must create a variable. The pointer should be of same type used in the malloc statement.Here we’ll make a pointer to a soon-to-be array of ints

malloc()分配請求大小的內(nèi)存，并返回指向已分配塊開頭的指針。 要保留此返回的指針，我們必須創(chuàng)建一個變量。 該指針應(yīng)與malloc語句中使用的類型相同。在這里，我們將創(chuàng)建一個指向即將成為整數(shù)的數(shù)組的指針。

int* arrayPtr;

Unlike other languages, C does not know the data type it is allocating memory for; it needs to be told. Luckily, C has a function called sizeof() that we can use.

與其他語言不同，C不知道它為其分配內(nèi)存的數(shù)據(jù)類型。 它需要被告知。 幸運(yùn)的是，C有一個我們可以使用的名為sizeof()的函數(shù)。

arrayPtr = (int *)malloc(10 * sizeof(int));

This statement used malloc to set aside memory for an array of 10 integers. As sizes can change between computers, it’s important to use the sizeof() function to calculate the size on the current computer.

該語句使用malloc為10個整數(shù)的數(shù)組留出內(nèi)存。 由于大小可以在計(jì)算機(jī)之間改變，因此使用sizeof()函數(shù)計(jì)算當(dāng)前計(jì)算機(jī)上的大小非常重要。

Any memory allocated during the program’s execution will need to be freed before the program closes. To free memory, we can use the free() function

在程序關(guān)閉之前，必須先釋放程序執(zhí)行期間分配的所有內(nèi)存。 要free內(nèi)存，我們可以使用free()函數(shù)

free( arrayPtr );

This statement will deallocate the memory previously allocated. C does not come with a garbage collector like some other languages, such as Java. As a result, memory not properly freed will continue to be allocated after the program is closed.

該語句將取消分配先前分配的內(nèi)存。 C沒有像Java之類的其他語言那樣帶有g(shù)arbage collector 。 因此，關(guān)閉程序后，將繼續(xù)分配未正確釋放的內(nèi)存。

在繼續(xù)之前... (Before you go on…)

回顧 (A Review)

• Malloc is used for dynamic memory allocation and is useful when you don’t know the amount of memory needed during compile time.
  Malloc用于動態(tài)內(nèi)存分配，當(dāng)您在編譯時不知道所需的內(nèi)存量時很有用。
• Allocating memory allows objects to exist beyond the scope of the current block.
  分配內(nèi)存允許對象存在于當(dāng)前塊的范圍之外。
• C passes by value instead of reference. Using malloc to assign memory, and then pass the pointer to another function, is more efficient than having the function recreate the structure.
  C通過值而不是引用傳遞。 使用malloc分配內(nèi)存，然后將指針傳遞給另一個函數(shù)，比讓函數(shù)重新創(chuàng)建結(jié)構(gòu)更有效。

有關(guān)C編程的更多信息： (More info on C Programming:)

• The beginner's handbook for C programming

  C程序設(shè)計(jì)初學(xué)者手冊

• If...else statement in C explained

  如果...在C中的其他語句解釋了

• Ternary operator in C explained

  C中的三元運(yùn)算符說明

翻譯自: https://www.freecodecamp.org/news/malloc-in-c-dynamic-memory-allocation-in-c-explained/

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