malloc语法 [英] malloc syntax

问题描述

Hello all


下面的方法1和方法2有什么区别？方法2是否可以安全使用？

typedef短字;

typedef unsigned char Char;


int nAllocSize = large number;


//方法1在我的机器中崩溃以获得大nAllocSize

Word * pShort =（Word *）malloc（nAllocSize * sizeof（Word））;


//方法2似乎没问题，即使nAllocSize很大

Word * pShort;

Char * pChar =（Char *） malloc（nAllocSize * sizeof（Char）* 2）;

pShort =（Word *）pChar;

解决方案

In < 48 ************************** @ posting.google.com> pe******@hotmail.com （pertheli）写道：

下面的方法1和方法2有什么区别？方法2是否可以安全使用？

typedef短字;
typedef unsigned char Char;

int nAllocSize =大数;

//方法1在我的机器中崩溃以获得大的nAllocSize
Word * pShort =（Word *）malloc（nAllocSize * sizeof（Word））;

//即使nAllocSize，方法2似乎也没问题很大
Word * pShort;
Char * pChar =（Char *）malloc（nAllocSize * sizeof（Char）* 2）;
pShort =（Word *）pChar;

如果sizeof（Word）== 2，这两种方法完全相同。

然而，正确的做法是：


size_t size = nAllocSize * sizeof * pShort;


if（size< nAllocSize || size< sizeof * pShort）{

/ *我们想要分配比size_t更多的字节可以代表* /

}


pShort = malloc（size）;

Dan

-

Dan Pop

DESY Zeuthen，RZ集团

电子邮件： Da ***** @ ifh.de

" pertheli" < PE ****** @ hotmail.com> schrieb im Newsbeitrag

news：48 ************************** @ posting.google.c om ...

Hello all

下面的方法1和方法2有什么区别？方法2
是否可以安全使用？

typedef短字;
typedef unsigned char Char;


为什么？

short和char有什么问题？

每个C程序员都知道这些类型，所以typedef只是在代码中添加噪声，并迫使维护者查看typedef ...

int nAllocSize =大数;

/ /方法1在我的机器中崩溃以获得大的nAllocSize
Word * pShort =（Word *）malloc（nAllocSize * sizeof（Word））;


#include< stdlib.h>

并将其设为

short * short_array = malloc（< large number> * sizeof * short_array）;

你是_sure_你的实现中的sizeof（短）== 2 ??

方法1崩溃和方法2成功建议否则。

//即使nAllocSize很大，方法2似乎也没问题
Word * pShort;
Char * pChar =（Char *）malloc（nAllocSize * sizeof（Char）* 2）;

char * other_array = malloc（（< large number> * sizeof * other_array * 2）;

如果sizeof（短）> ; 2你使用malloc（）ed空间你可能会

触发WW3


这两种方法是_not_ repeat _not_等效。

Robert

pe ****** @ hotmail.com （pertheli）在留言新闻中写道：< 48 ************************** @ posting.google。 com> ...

大家好。

下面的方法1和方法2有什么区别？方法2是否可以安全使用？

typedef短字;
typedef unsigned char Char;

int nAllocSize =大数字;

//方法1在我的机器中崩溃以获得大的nAllocSize
Word * pShort =（Word *）malloc（nAllocSize * sizeof（Word））;


失去演职员表。你不需要它（在C中，无论如何），如果你没有malloc的原型（）

可以抑制诊断b范围内（即你忘了#include stdlib.h - 你*记得

到#include stdlib.h，对吧？）。


Word * pShort = malloc（nAllocSize * sizeof * pShort）;


同样适用，看起来更清洁。


至于为什么一个人在另一个人没有崩溃时崩溃，我不知道。提供

sizeof（短）== 2 * sizeof（char），他们应该分配相同的

空间量。

//方法即使nAllocSize很大，2似乎也没问题
Word * pShort;
Char * pChar =（Char *）malloc（nAllocSize * sizeof（Char）* 2）;
pShort =（Word *） pChar;

Hello all

What is the difference between Method 1 and Method 2 below? Is Method 2 safe to use?
typedef short Word;
typedef unsigned char Char;

int nAllocSize = large number;

//Method 1 crashes in my machine for large nAllocSize
Word* pShort = (Word*)malloc(nAllocSize*sizeof(Word));

//Method 2 seems ok even if nAllocSize is large
Word* pShort;
Char* pChar = (Char*)malloc(nAllocSize*sizeof(Char)*2);
pShort = (Word*)pChar;

解决方案

In <48**************************@posting.google.com > pe******@hotmail.com (pertheli) writes:

What is the difference between Method 1 and Method 2 below? Is Method 2 safe to use?

typedef short Word;
typedef unsigned char Char;

int nAllocSize = large number;

//Method 1 crashes in my machine for large nAllocSize
Word* pShort = (Word*)malloc(nAllocSize*sizeof(Word));

//Method 2 seems ok even if nAllocSize is large
Word* pShort;
Char* pChar = (Char*)malloc(nAllocSize*sizeof(Char)*2);
pShort = (Word*)pChar;

If sizeof(Word) == 2, the two methods are perfectly equivalent.
The right way of doing it, however, is:

size_t size = nAllocSize * sizeof *pShort;

if (size < nAllocSize || size < sizeof *pShort) {
/* we want to allocate more bytes than size_t can represent */
}

pShort = malloc(size);
Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

"pertheli" <pe******@hotmail.com> schrieb im Newsbeitrag
news:48**************************@posting.google.c om...

Hello all

What is the difference between Method 1 and Method 2 below? Is Method 2 safe to use?

typedef short Word;
typedef unsigned char Char;
Why??
What''s wrong with short and char?
Every C programmer knows these types and so the typedefs just add noise to
the code and force a maintainer to look the typedefs up...

int nAllocSize = large number;

//Method 1 crashes in my machine for large nAllocSize
Word* pShort = (Word*)malloc(nAllocSize*sizeof(Word));
#include <stdlib.h>
and make that
short *short_array = malloc(<large number> * sizeof *short_array);
Are you _sure_ that sizeof(short) == 2 in your implementation??
Method 1 crashing and Method 2 succeeding suggests otherwise.

//Method 2 seems ok even if nAllocSize is large
Word* pShort;
Char* pChar = (Char*)malloc(nAllocSize*sizeof(Char)*2);

char *other_array = malloc((<large number> * sizeof *other_array * 2);
And if sizeof(short) > 2 and you use the malloc()ed space you will probably
trigger WW3

The two methods are _not_ repeat _not_ equivalent.
Robert

pe******@hotmail.com (pertheli) wrote in message news:<48**************************@posting.google. com>...

Hello all

What is the difference between Method 1 and Method 2 below? Is Method 2 safe to use?
typedef short Word;
typedef unsigned char Char;

int nAllocSize = large number;

//Method 1 crashes in my machine for large nAllocSize
Word* pShort = (Word*)malloc(nAllocSize*sizeof(Word));
Lose the cast. You don''t need it (in C, anyway), and having it there
could supress a diagnostic if you don''t have a prototype for malloc()
in scope (i.e., you forgot to #include stdlib.h -- you *did* remember
to #include stdlib.h, right?).

Word *pShort = malloc (nAllocSize * sizeof *pShort);

works just as well, and is a little cleaner to look at.

As to why one crashes when the other doesn''t, I don''t know. Provided
sizeof (short) == 2 * sizeof (char), they should allocate the same
amount of space.

//Method 2 seems ok even if nAllocSize is large
Word* pShort;
Char* pChar = (Char*)malloc(nAllocSize*sizeof(Char)*2);
pShort = (Word*)pChar;

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