blocks|key|675647|text|当将值传递给函数参数时，C中有两件事|type|unstyled|depth|inlineStyleRanges|entityRanges|data|675648|按值传递|ordered-list-item|675649|参照通过|675650|您正在按值传递，因此您将一些未初始化的值传递给该函数，并在函数之外不可见的函数中初始化它，您正在尝试在main()中使用未初始化的值，这将导致未定义的行为。|offset|length|style|CODE|675651|arg+=+"0123456789";|code-block|syntax|javascript|675652|如果要将字符串复制到某个内存位置，则需要memcpy()或strcpy()。|675653|注意:使用未初始化的值会导致未定义的行为。|675654|entityMap^0|0|0|0|1F|6|0|0|K|8|T|8|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Y|8|@]|9|@]|A|$]]|$1|E|3|F|5|D|7|Z|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|10|8|@$I|11|J|12|K|L]]|9|@]|A|$]]|$1|M|3|N|5|O|7|13|8|@]|9|@]|A|$P|Q]]|$1|R|3|S|5|6|7|14|8|@$I|15|J|16|K|L]|$I|17|J|18|K|L]]|9|@]|A|$]]|$1|T|3|U|5|6|7|19|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|W|$]]

There are 2 things in C when it comes to passing the value to function parameters

<ol>
<li>Pass by value</li>
<li>Pass by reference</li>
</ol>

You are doing pass by value so you are passing some unintiialized value to the function and initializing it in the function which is not visible outside the function, you are trying to use uninitialized values in <code>main()</code> which will lead to undefined behavior.

<pre><code>arg = "0123456789";
</code></pre>

If you want to copy a string to some memory location then you need <code>memcpy()</code> or <code>strcpy()</code>

Note: Using uninitialized values leads to undefined behavior.

blocks|key|294864|text|您的代码有几个问题。这是固定代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|294865|/*+Don't+forget+to+include+<stdio.h>,+<stdlib.h>+and+<string.h>+*/

typedef+struct+{
++++char+*a;
++++char+*b;
++++char+*c;
}mystruct;

void+init_chars+(char+**arg)+/*+This+should+be+char**+as+the+address+of+a+char*+is+passed+*/
{
++++*arg+=+malloc+(+/*sizeof(char)*+*/+11);+/*+sizeof(char)+is+1+always.+You+don't+need+it+*/
++++++++++++++++++++++++++++++++++++++++++++/*+Note+the+change+of+`arg`+to+`*arg`+too+*/
++++++++++++++++++++++++++++++++++++++++++++/*+And+that+I've+used+11+and+not+10+because+there+needs+to+be+space+for+the+NUL-terminator+*/

++++if(*arg+==+NULL)+/*+If+the+above+malloc+failed+*/
++++{
++++++++printf("Oops!+malloc+for+*arg+failed!");
++++++++exit(-1);
++++}

++++//arg+=+"0123456789";+/*+You+just+lost+the+allocated+memory+as+you+make+the+pointer+point+to+a+string+literal+*/

++++strcpy(*arg,+"0123456789");+/*+Use+strcpy+instead+*/
++++printf+("%25s\n",+*arg);++++++/*+*arg+here+*/
}

int+main+()
{
++++mystruct+*msp+=+malloc+(sizeof+(mystruct));

++++if(msp+==+NULL)+/*+If+the+above+malloc+failed+*/
++++{
++++++++printf("Oops!+malloc+for+msp+failed!");
++++++++return+-1;
++++}

++++init_chars+(&(msp->a));
++++init_chars+(&(msp->b));+
++++init_chars+(&(msp->c));++/*+Pass+address+of+variables+rather+than+their+value+*/

++++printf+("%25s,+%25s,+%25s\n",+msp->a,+msp->b,+msp->c);

++++free(msp->a);
++++free(msp->b);
++++free(msp->c);

++++free(msp);++++/*+Free+everything+after+use+*/

++++return+0;
}|code-block|syntax|javascript|294866|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Your code has several problems. Here is the fixed code:

<pre><code>/* Don't forget to include &lt;stdio.h&gt;, &lt;stdlib.h&gt; and &lt;string.h&gt; */

typedef struct {
 char *a;
 char *b;
 char *c;
}mystruct;

void init_chars (char **arg) /* This should be char** as the address of a char* is passed */
{
 *arg = malloc ( /*sizeof(char)* */ 11); /* sizeof(char) is 1 always. You don't need it */
 /* Note the change of `arg` to `*arg` too */
 /* And that I've used 11 and not 10 because there needs to be space for the NUL-terminator */

 if(*arg == NULL) /* If the above malloc failed */
 {
 printf("Oops! malloc for *arg failed!");
 exit(-1);
 }

 //arg = "0123456789"; /* You just lost the allocated memory as you make the pointer point to a string literal */

 strcpy(*arg, "0123456789"); /* Use strcpy instead */
 printf ("%s\n", *arg); /* *arg here */
}

int main ()
{
 mystruct *msp = malloc (sizeof (mystruct));

 if(msp == NULL) /* If the above malloc failed */
 {
 printf("Oops! malloc for msp failed!");
 return -1;
 }

 init_chars (&amp;(msp-&gt;a));
 init_chars (&amp;(msp-&gt;b)); 
 init_chars (&amp;(msp-&gt;c)); /* Pass address of variables rather than their value */

 printf ("%s, %s, %s\n", msp-&gt;a, msp-&gt;b, msp-&gt;c);

 free(msp-&gt;a);
 free(msp-&gt;b);
 free(msp-&gt;c);

 free(msp); /* Free everything after use */

 return 0;
}
</code></pre>

blocks|key|208445|text|typedef+struct+{
++++char+*a;
++++char+*b;
++++char+*c;
}mystruct;

void+init_chars+(char+**arg)
{
++++*arg+=+malloc+(sizeof+(char)*11);
++++if(*arg+==+NULL)
++++{
++++++++printf("malloc+failed!");
++++++++exit(-1);
++++}
++++strcpy(*arg,"0123456789");
++++printf+("%25s\n",+*arg);
}

int+main+()
{
++++mystruct+*msp+=+malloc+(sizeof+(mystruct));
++++if(msp+==+NULL)
++++{
++++++++printf("malloc+failed");
++++++++exit(-1);
++++}
++++init_chars+(&msp->a);
++++init_chars+(&msp->b);
++++init_chars+(&msp->c);
++++printf+("%25s,+%25s,+%25s\n",+msp->a,+msp->b,+msp->c);
++++free(msp->a);
++++free(msp->b);
++++free(msp->c);
++++free(msp)
++++return+0;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|208446|产出：|unstyled|208447|0123456789|208448|208449|208450|0123456789,0123456789,0123456789|208451|与您的代码进行比较，您将了解为什么|208452|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|R|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|S|8|@]|9|@]|A|$]]|$1|I|3|H|5|F|7|T|8|@]|9|@]|A|$]]|$1|J|3|H|5|F|7|U|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|V|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|W|8|@]|9|@]|A|$]]|$1|O|3|-4|5|F|7|X|8|@]|9|@]|A|$]]]|P|$]]

<pre><code>typedef struct {
 char *a;
 char *b;
 char *c;
}mystruct;

void init_chars (char **arg)
{
 *arg = malloc (sizeof (char)*11);
 if(*arg == NULL)
 {
 printf("malloc failed!");
 exit(-1);
 }
 strcpy(*arg,"0123456789");
 printf ("%s\n", *arg);
}

int main ()
{
 mystruct *msp = malloc (sizeof (mystruct));
 if(msp == NULL)
 {
 printf("malloc failed");
 exit(-1);
 }
 init_chars (&amp;msp-&gt;a);
 init_chars (&amp;msp-&gt;b);
 init_chars (&amp;msp-&gt;c);
 printf ("%s, %s, %s\n", msp-&gt;a, msp-&gt;b, msp-&gt;c);
 free(msp-&gt;a);
 free(msp-&gt;b);
 free(msp-&gt;c);
 free(msp)
 return 0;
}
</code></pre>

output:

0123456789

0123456789

0123456789

0123456789, 0123456789, 0123456789

compare with your code u will understand why

This is more out of curiosity, and is not how I want or need it to work. But when I was doing some mockups and wanted to test something out, I ended up with something like this... and was wondering why it doesn't work as I expected. 

<pre><code>typedef struct {
 char *a;
 char *b;
 char *c;
}mystruct;

void init_chars (char *arg)
{
 arg = malloc (sizeof (char)*10);
 arg = "0123456789";
 printf ("%s\n", arg);
}

int main ()
{
 mystruct *msp = malloc (sizeof (mystruct));
 init_chars (msp-&gt;a);
 init_chars (msp-&gt;b);
 init_chars (msp-&gt;c);
 printf ("%s, %s, %s\n", msp-&gt;a, msp-&gt;b, msp-&gt;c);
 return 0;
}
</code></pre>

Prints...

<pre class="lang-none prettyprint-override"><code>0123456789

0123456789

0123456789

(null),(null),(null)
</code></pre>

Struct member char * initialized in a function call as a parameter

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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这更多的是出于好奇，而不是我希望或需要它的工作方式。但当我做一些模特儿想测试一些东西的时候，我最终得到了这样的结果.不知道为什么不像我预料的那样起作用。typedef struct {    char *a;    char *b;    char *c;}mystruct;void init_chars (char ...

问函数调用中初始化为参数的Struct成员char *
EN

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问函数调用中初始化为参数的Struct成员char *EN