blocks|key|5972490|text|RequestInfo[1]+=+"1";|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|5972491|并不是像你想的那样做。要么就是|unstyled|5972492|RequestInfo[1].string+=+"1";|5972493|如果RequestInfo是至少包含2个元素的MqlStr对象的向量，或者|offset|length|style|CODE|5972494|RequestInfo->string+=+"1";|5972495|如果RequestInfo是指向单个MqlStr对象的指针。|5972496|entityMap^0|0|0|0|2|B|N|6|0|0|2|B|I|6|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|V|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|X|8|@$K|Y|L|Z|M|N]|$K|10|L|11|M|N]]|9|@]|A|$]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$B|C]]|$1|Q|3|R|5|F|7|13|8|@$K|14|L|15|M|N]|$K|16|L|17|M|N]]|9|@]|A|$]]|$1|S|3|-4|5|F|7|18|8|@]|9|@]|A|$]]]|T|$]]

<pre><code>RequestInfo[1] = "1";
</code></pre>

is not doing what you think. It's either

<pre><code>RequestInfo[1].string = "1";
</code></pre>

if <code>RequestInfo</code> is a vector of <code>MqlStr</code> objects containing at least 2 elements, or

<pre><code>RequestInfo-&gt;string = "1";
</code></pre>

if <code>RequestInfo</code> is a pointer to a single <code>MqlStr</code> object.

blocks|key|3296134|text|您是否为RequestInfo元素中的.string指针分配了足够的空间？strncpy没有为您分配空间，请使用strdup来分配空间。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3296135|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Have you allocated enough space for the .string pointers in your RequestInfo elements? strncpy is not allocating the space for you, use strdup for that.

blocks|key|3296153|text|您需要以安全的方式管理MqlStr内存，这可以通过使用std::string等标准容器或通过编写方法来分配和释放内存来实现。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3296154|下面是一个管理其内部内存的简单类的示例：|3296155|#include+<cstdlib>
#include+<iostream>
#include+<string.h>
#include+<sstream>

struct+MqlStr
{
public:
++++int++++len;
++++char++*string;

++++MqlStr()+{+init+++();+}
+++~MqlStr()+{+dealloc();+}
++++void+assign(std::string&+str)+{
++++++++dealloc();
++++++++string+=+new+char[str.length()+%2B+1];
++++++++strncpy(string,+str.c_str(),+str.length());
++++++++string[str.length()]+=+0;
++++++++len+=+str.length();
++++}
++++void+dealloc()+{
++++++++if(string+!=+0)+delete+[]+string;+init();
++++}

private:
++++void+init()+{+string+=+0;+len+=+0;+}
+++++++++MqlStr(const+MqlStr+&);
++++void+operator=+(const+MqlStr+&);
};

double+CheckExecutionRequests(MqlStr*+RequestInfo)
{
++++static+int+callCount+=+0;
++++std::ostringstream+stringstream;+stringstream<<"callCount:+"<<callCount%2B%2B;
++++std::string+field1+=+stringstream.str();
++++RequestInfo->assign(field1);
++++return+1.0;
}

int+main(int+argc,+char**+argv)
{
++++MqlStr+s[5];

++++std::cout<<"First+call"<<std::endl;
++++for(unsigned+i+=+0;+i+<+sizeof(s)/sizeof(s[0]);+%2B%2Bi)
++++++++CheckExecutionRequests(s+%2B+i);

++++for(unsigned+i+=+0;+i+<+sizeof(s)/sizeof(s[0]);+%2B%2Bi)
++++++++std::cout<<"MqlStr["<<i<<"].string+=+"<<s[i].string<<std::endl;

++++std::cout<<"Second+call"<<std::endl;
++++for(unsigned+i+=+0;+i+<+sizeof(s)/sizeof(s[0]);+%2B%2Bi)
++++++++CheckExecutionRequests(s+%2B+i);

++++for(unsigned+i+=+0;+i+<+sizeof(s)/sizeof(s[0]);+%2B%2Bi)
++++++++std::cout<<"MqlStr["<<i<<"].string+=+"<<s[i].string<<std::endl;

++++return+EXIT_SUCCESS;
}|code-block|syntax|javascript|3296156|使用相同的MqlStr实例第二次执行CheckExecutionRequests不会损坏内存。代码的扩展可以是字符串大小的预分配，并且仅当新的str.length+>+this.maxLength+(预分配的长度与字符串大小不同)时才在assign方法中重新分配内存。复制构造函数和赋值运算符当前被禁用，因为在管理堆上的内部内存时，如果它们没有正确实现，可能会导致问题。|3296157|更简单的解决方案是使用标准容器编写结构，如下所示：|3296158|struct+MqlStr
{
public:
++++std::string+string;
}|3296159|然后将您为字段获得的字符串分配给MqlStr字符串。|3296160|entityMap^0|B|6|R|B|0|0|0|0|0|0|G|6|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|12|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|13|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|14|8|@]|D|@]|E|$]]|$1|Q|3|R|5|J|7|15|8|@]|D|@]|E|$K|L]]|$1|S|3|T|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|U|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|V|$]]

You need to manage <code>MqlStr</code> memory in a safe manner, this can happen by using a standard container like <code>std::string</code> or by writing methods to allocate and deallocate the internal memory.

Here is an example of a simple class that manages its internal memory:

<pre><code>#include &lt;cstdlib&gt;
#include &lt;iostream&gt;
#include &lt;string.h&gt;
#include &lt;sstream&gt;

struct MqlStr
{
public:
 int len;
 char *string;

 MqlStr() { init (); }
 ~MqlStr() { dealloc(); }
 void assign(std::string&amp; str) {
 dealloc();
 string = new char[str.length() + 1];
 strncpy(string, str.c_str(), str.length());
 string[str.length()] = 0;
 len = str.length();
 }
 void dealloc() {
 if(string != 0) delete [] string; init();
 }

private:
 void init() { string = 0; len = 0; }
 MqlStr(const MqlStr &amp;);
 void operator= (const MqlStr &amp;);
};

double CheckExecutionRequests(MqlStr* RequestInfo)
{
 static int callCount = 0;
 std::ostringstream stringstream; stringstream&lt;&lt;"callCount: "&lt;&lt;callCount++;
 std::string field1 = stringstream.str();
 RequestInfo-&gt;assign(field1);
 return 1.0;
}

int main(int argc, char** argv)
{
 MqlStr s[5];

 std::cout&lt;&lt;"First call"&lt;&lt;std::endl;
 for(unsigned i = 0; i &lt; sizeof(s)/sizeof(s[0]); ++i)
 CheckExecutionRequests(s + i);

 for(unsigned i = 0; i &lt; sizeof(s)/sizeof(s[0]); ++i)
 std::cout&lt;&lt;"MqlStr["&lt;&lt;i&lt;&lt;"].string = "&lt;&lt;s[i].string&lt;&lt;std::endl;

 std::cout&lt;&lt;"Second call"&lt;&lt;std::endl;
 for(unsigned i = 0; i &lt; sizeof(s)/sizeof(s[0]); ++i)
 CheckExecutionRequests(s + i);

 for(unsigned i = 0; i &lt; sizeof(s)/sizeof(s[0]); ++i)
 std::cout&lt;&lt;"MqlStr["&lt;&lt;i&lt;&lt;"].string = "&lt;&lt;s[i].string&lt;&lt;std::endl;

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

The second execution of CheckExecutionRequests with the same MqlStr instances will not corrupt the memory. 
An extension to the code can be preallocation of the string size, and only reallocating the memory in the assign method if the new str.length > this.maxLength (preallocated length different from the string size).
The copy constructor and assignment operator are currently disabled, because they can cause problems if not implemented properly while managing internal memory on the heap.

A simpler solution would be to write your struct using a standard container as follows:

<pre><code>struct MqlStr
{
public:
 std::string string;
}
</code></pre>

And then just assign the string you get for the fields to <code>MqlStr</code> string.

I have been pulling my hair out on this particular issue and would like some advice. I have the following struct:

<pre><code>struct MqlStr // MQL String Array
{
int len;
char *string;
};
</code></pre>

this is being passed to a function as a pointer from an external application as such:

<pre><code>MT4_EXPFUNC double __stdcall CheckExecutionRequests(MqlStr* RequestInfo)
</code></pre>

within the function i am generating a number of string values that i need to assign to varies elements of the MqlStr array. the following works fine:

<pre><code>RequestInfo[1].string = "1";
RequestInfo[2].string = "2";
</code></pre>

but when i use strcpy to get my generated string value into the array, it overwrites the entire array with the value i copied. for example:

<pre><code>string field1 = value.substr(Demark + 1, Demark2 - Demark - 1);
strncpy(RequestInfo[1].string, field1.c_str(), field1.size());

string field2 = value.substr(Demark + 1, Demark2 - Demark - 1);
strncpy(RequestInfo[2].string, field2.c_str(), field2.size());
</code></pre>

if field1 = 1 and field2 = 2 then the entire RequestInfo[] array would be equal to 2 (the last value copied)

can someone point me in the right direction?

C++ string to char* array struct

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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在这个特定的问题上，我一直在绞尽脑汁，我想要一些建议。我有以下结构：struct MqlStr // MQL String Array{int               len;char              *string;};这将作为指针从外部应用程序传递给函数，如下所示：MT4_EXPFUNC double...

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