malloc结构？ [英] malloc a struct?
问题描述
大家好..
如果我想要malloc一个结构，请说如下：
struct myStruct1
{
int number;
char * string;
}
怎么样我这样做了吗？
我需要首先使用malloc myStruct，然后是malloc字符串吗？
我见过一些malloc命令，所以：
myStruct1 = malloc（sizeof（myStruct1））;
myStruct1 = malloc（sizeof（* myStruct1））;
myStruct1 = malloc（sizeof（myStruct1 *））;
有谁能告诉我差异吗？
谢谢大家的帮助！非常感谢！
mike79
mi **** @ iprimus.com.au （mike79）写道：
如果我想要malloc一个结构，请说明以下内容：
struct myStruct1
{
int number;
char * string;
}
我该怎么做？
struct myStruct1 * s = malloc（sizeof * s）;
之后，你可以分配给s->分配的字符串内存对于
字符串，请说像
s-> string = malloc（strlen（myString）+ 1）;
我会首先需要malloc myStruct，然后是malloc字符串？
这是最简单的方法。你绝对不能将
分配给一个尚未分配
的结构对象的字符串成员，尽管你可以为
string。
我见过一些malloc命令，所以是：
C没有命令。 malloc（）是标准
C库中的函数。
myStruct1 = malloc（sizeof（myStruct1））;
根据你上面的
定义，你必须是sizeof（struct myStruct1）。
另外，将结构和指针命名为结构'myStruct1'的对象是令人困惑的。
调用时malloc（），我建议在你分配的对象上使用sizeof运算符，而不是在类型上。例如，
*不要写这个：
int * x = malloc（sizeof（int）* 128）; / *不要这样做！ * /
相反，请这样写：
int * x = malloc（sizeof * x * 128）;
这样做有几个理由：
*如果你改变了'x'指向的类型，它'''更改malloc（）调用也不需要
。
这在大型程序中更是一个问题，但它仍然是
方便小一点。
*考虑一个对象的大小使得编写语句
不易出错。您可以验证sizeof语法是否正确无需查看声明。
myStruct1 = malloc（sizeof（* myStruct1））;
这样更好，虽然我再给结构和
对象不同的名字。
myStruct1 = malloc（sizeof（myStruct1 *））;
错误。
-
int main（void ）{char p [] =" ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuv wxyz。\
\ n"，* q =" kl BIcNBFr.NKEzjwCIxNJC" ;; int i = sizeof p / 2; char * strchr（ ）; int putchar（\
）; while（* q）{i + = strchr（p，* q ++） - p; if（i> =（int）sizeof p）i- = sizeof p-1; putchar（p [i] \
）;}返回0;}
更好地定义这样的结构：
typedef struct {
int number;
char * string;
} myStruct1;
到malloc你可以这样做，创建你的指针。
myStruct1 * name =（myStruct *）malloc （sizeof（myStruct1））;
你应该检查malloc是否也返回null也是为了错误
处理
引用结构指针中的元素只需使用这种语法。
name-> number = x;
和malloc结构中的指针：
name-> string = malloc（数字）;
数字是你想要的字符
- >当你处理指向结构的指针时使用它，否则它通常是''structname.structmember''语法。
" mike79" < MI **** @ iprimus.com.au>在消息中写道
新闻：49 ************************* @ posting.google.co m ... < blockquote class =post_quotes>大家好..
如果我想要malloc一个结构，请说如下：
struct myStruct1
{
int number;
char * string;
}
我该怎么做？
我需要首先使用malloc myStruct，然后是malloc字符串吗？
我看过一些malloc命令，所以是：
myStruct1 = malloc（sizeof（myStruct1））;
myStruct1 = malloc（sizeof（* myStruct1）） ;
myStruct1 = malloc（sizeof（myStruct1 *））;
有谁能告诉我差异吗？
谢谢大家的帮助！非常感谢！
mike79
[top-posting更正]
Jason写道：
" mike79" < MI **** @ iprimus.com.au>在消息中写道
新闻：49 ************************* @ posting.google.co m ...
< blockquote class =post_quotes>大家好..
如果我想要malloc一个结构，请说如下：
struct myStruct1
{
int number;
char * string;
}
我该怎么做？
我需要首先使用malloc myStruct，然后是malloc字符串吗？
我看过一些malloc命令，所以是：
myStruct1 = malloc（sizeof（myStruct1））;
myStruct1 = malloc（sizeof（* myStruct1）） ;
myStruct1 = malloc（sizeof（myStruct1 *））;
有谁能告诉我差异吗？
谢谢大家的帮助！非常感谢！
更好地定义这样的结构：
typedef struct {
int number;
char * string;
} myStruct1 ;对于malloc，你可以这样做，创建你的指针。
myStruct1 * name =（myStruct *）malloc（sizeof（myStruct1））;
演员是不必要的，可以隐藏失败的错误
#include< stdlib.h>
风格上，这会更好：
myStruct1 * name = malloc（sizeof * name）;
as，如果类型应该碰巧改变了，你只需要在* one *的地方更改它
。
你应该检查一下malloc是否也为
错误返回null处理
引用struct指针中的元素只需使用这个
语法。 name-> number = x;
和malloc结构中的指针：
name-> string = malloc（number）;
数字是字符你想要
当然，你应该真的这样：
name-> string = malloc（number + 1）;
来说明C风格字符串中的尾随空字符。
- >在你处理结构
的指针时使用，否则它是通常的''structname.structmember''语法。
HTH，
- g
-
Artie Gold - 德克萨斯州奥斯汀
哦，对于过去的美好时光老垃圾邮件。
hi all..
if I wanted to malloc a struct, say the following:
struct myStruct1
{
int number;
char *string;
}
how would I do this?
Would I need to first malloc myStruct, then malloc string?
Ive seen some malloc commands around, so are:
myStruct1 = malloc(sizeof (myStruct1));
myStruct1 = malloc(sizeof (* myStruct1));
myStruct1 = malloc(sizeof (myStruct1 *));
Can anyone tell me the difference please??
Thank you all for your help! much appreciated!
mike79
mi****@iprimus.com.au (mike79) writes:
if I wanted to malloc a struct, say the following:
struct myStruct1
{
int number;
char *string;
}
how would I do this?
struct myStruct1 *s = malloc (sizeof *s);
After that, you can assign to s->string memory allocated for the
string, say with something like
s->string = malloc (strlen (myString) + 1);
Would I need to first malloc myStruct, then malloc string?
That''s the most straightforward approach. You definitely can''t
assign to the string member of a structure object that hasn''t yet
been allocated, although you could allocate the memory for the
string.
Ive seen some malloc commands around, so are:
C doesn''t have commands. malloc() is a function in the standard
C library.
myStruct1 = malloc(sizeof (myStruct1));
That''d have to be sizeof (struct myStruct1) based on your
definition above.
Also, it is confusing to name both the structure and a pointer to
an object of the structure''s type `myStruct1''.
When calling malloc(), I recommend using the sizeof operator on
the object you are allocating, not on the type. For instance,
*don''t* write this:
int *x = malloc (sizeof (int) * 128); /* Don''t do this! */
Instead, write it this way:
int *x = malloc (sizeof *x * 128);
There''s a few reasons to do it this way:
* If you ever change the type that `x'' points to, it''s not
necessary to change the malloc() call as well.
This is more of a problem in a large program, but it''s still
convenient in a small one.
* Taking the size of an object makes writing the statement
less error-prone. You can verify that the sizeof syntax is
correct without having to look at the declaration.
myStruct1 = malloc(sizeof (* myStruct1));
That''s better, although again I''d give the structure and the
object different names.
myStruct1 = malloc(sizeof (myStruct1 *));
Wrong.
--
int main(void){char p[]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuv wxyz.\
\n",*q="kl BIcNBFr.NKEzjwCIxNJC";int i=sizeof p/2;char *strchr();int putchar(\
);while(*q){i+=strchr(p,*q++)-p;if(i>=(int)sizeof p)i-=sizeof p-1;putchar(p[i]\
);}return 0;}
better to define struct like this:
typedef struct {
int number;
char *string;
}myStruct1;
to malloc you can do this, creating your pointer.
myStruct1 *name = (myStruct *) malloc(sizeof(myStruct1));
you are supposed to check to see if malloc returns null also for error
handling
to reference elements within your struct pointer just use this syntax.
name->number = x;
and to malloc the pointer within the struct:
name->string = malloc(number);
number being characters u want
-> is used when u are dealing with a pointer to a structure otherwise its
the usual ''structname.structmember'' syntax.
"mike79" <mi****@iprimus.com.au> wrote in message
news:49*************************@posting.google.co m...hi all..
if I wanted to malloc a struct, say the following:
struct myStruct1
{
int number;
char *string;
}
how would I do this?
Would I need to first malloc myStruct, then malloc string?
Ive seen some malloc commands around, so are:
myStruct1 = malloc(sizeof (myStruct1));
myStruct1 = malloc(sizeof (* myStruct1));
myStruct1 = malloc(sizeof (myStruct1 *));
Can anyone tell me the difference please??
Thank you all for your help! much appreciated!
mike79
[top-posting corrected]
Jason wrote:
"mike79" <mi****@iprimus.com.au> wrote in message
news:49*************************@posting.google.co m...hi all..
if I wanted to malloc a struct, say the following:
struct myStruct1
{
int number;
char *string;
}
how would I do this?
Would I need to first malloc myStruct, then malloc string?
Ive seen some malloc commands around, so are:
myStruct1 = malloc(sizeof (myStruct1));
myStruct1 = malloc(sizeof (* myStruct1));
myStruct1 = malloc(sizeof (myStruct1 *));
Can anyone tell me the difference please??
Thank you all for your help! much appreciated!better to define struct like this:
typedef struct {
int number;
char *string;
}myStruct1;
to malloc you can do this, creating your pointer.
myStruct1 *name = (myStruct *) malloc(sizeof(myStruct1));
The cast is unnecessary and can hide the error of failing to
#include <stdlib.h>
Stylistically, this would be better:
myStruct1 *name = malloc(sizeof *name);
as, if the type should happen to change, you only need to change it
in *one* place.
you are supposed to check to see if malloc returns null also for error handling
to reference elements within your struct pointer just use this syntax. name->number = x;
and to malloc the pointer within the struct:
name->string = malloc(number);
number being characters u want
Of course, you should really make that:
name->string = malloc(number + 1);
to account for the trailing null character in C-style strings.
-> is used when u are dealing with a pointer to a structure otherwise its the usual ''structname.structmember'' syntax.
HTH,
--ag
--
Artie Gold -- Austin, Texas
Oh, for the good old days of regular old SPAM.
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