{"id":99,"date":"2013-08-06T11:01:55","date_gmt":"2013-08-06T11:01:55","guid":{"rendered":"https:\/\/praveenkatiyar.wordpress.com\/?p=99"},"modified":"2013-08-06T11:01:55","modified_gmt":"2013-08-06T11:01:55","slug":"modifying-array-of-structures-default-marshaling","status":"publish","type":"post","link":"https:\/\/praveenkatiyar.in\/blog\/index.php\/2013\/08\/06\/modifying-array-of-structures-default-marshaling\/","title":{"rendered":"Modifying array of structures (default marshaling)"},"content":{"rendered":"

Let\u2019s assume you have a user defined structure \u201cEMPLOYEE<\/font><\/strong>\u201d in a win32 DLL (let say it \u201cWin32Native.dll<\/strong>\u201d) as shown below.<\/p>\n

typedef struct _EMPLOYEE
{
    int Age ;
    int Sex;
    double Salary ;
    char* FirstName ;
    char* LastName ;
} EMPLOYEE;
<\/strong><\/font><\/p>\n

Define some functions in native dll (let say it \u201cWin32Native.dll<\/strong>\u201d)  as shown below.  <\/p>\n

extern "C" __declspec(dllexport) void <\/font><\/font>ModifyArrayOfEmployeeStruct(int nSize, EMPLOYEE* pArray);<\/font><\/strong><\/font><\/font><\/p>\n

Implementing Functions<\/h3>\n

extern "C" __declspec(dllexport) void ModifyArrayOfEmployeeStruct( int nSize, EMPLOYEE* pArray)
{
    int result = 0;
    EMPLOYEE* pCur = pArray;
    STRSAFE_LPSTR temp1, temp2 ;
<\/strong><\/font>    for ( int i = 0; i < nSize; i++ )
    {
        size_t nLen1 = 0;
        size_t nLen2 = 0;
        StringCchLengthA( pCur->FirstName, STRSAFE_MAX_CCH, &nLen1 );
        StringCchLengthA( pCur->LastName, STRSAFE_MAX_CCH, &nLen2 );
       
        nLen1 = sizeof(char) * ( nLen1 + 11 );    \/\/    To accomodate "<Modified>"
        nLen2 = sizeof(char) * ( nLen2 + 11 );    \/\/    To accomodate "<Modified>"
        temp1 = (STRSAFE_LPSTR)CoTaskMemAlloc( nLen1 );
        temp2 = (STRSAFE_LPSTR)CoTaskMemAlloc( nLen2 );<\/strong><\/font><\/p>\n

        StringCchCopyA( temp1, nLen1, (STRSAFE_LPCSTR)"<Modified>" );
        StringCbCatA( temp1, nLen1, (STRSAFE_LPCSTR)pCur->FirstName);<\/strong><\/font><\/p>\n

        StringCchCopyA( temp2, nLen2, (STRSAFE_LPCSTR)"<Modified>" );
        StringCbCatA( temp2, nLen2, (STRSAFE_LPCSTR)pCur->LastName);
               
        \/\/ CoTaskMemFree must be used instead of delete to free memory.
        CoTaskMemFree( pCur->FirstName  );
        CoTaskMemFree( pCur->LastName  );<\/strong><\/font><\/p>\n

        pCur->FirstName = (char *)temp1;
        pCur->LastName = (char *)temp2;<\/strong><\/font><\/p>\n

        pCur->Age += 1 ;
        pCur->Salary  += 1000.0 ;
        pCur++;
   }
}<\/strong><\/font><\/p>\n

<\/strong><\/p>\n

Point of Interest<\/h4>\n
  • CoTaskMemAlloc is used to allocated the memory required. <\/strong><\/li>\n
  • CoTaskMemFree <\/strong>is used to free any previously allocated buffer, if null is passed then, CoTaskMemFree <\/strong>is not called.<\/strong> <\/li>\n
  • StringCchCopyA<\/strong> copies an ANSI string to a string buffer. <\/li>\n
  • StringCbCatA<\/strong> Appends an ANSI string to a string buffer.\n

    If you want to use a heap that is shared between native and managed<\/strong>, it is more common to use the COM heap. <\/p>\n<\/li>\n

  • On the native side use CoTaskMemAlloc()<\/strong><\/code><\/a> and CoTaskMemFree()<\/strong><\/code><\/a>.\n

     <\/p>\n

    Writing the client code (the managed part) <\/h4>\n

    one can simple create a console base application which can use this dll. let\u2019s name it MarshallingTest. <\/strong><\/p>\n

    see the code snippet below.<\/p>\n

    using System;
    using System.Runtime.InteropServices;
    using System.Text;<\/strong><\/font><\/p>\n

    namespace MarshallingTest
    {<\/strong><\/font><\/p>\n

        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
        public struct Employee
        {
            public int Age;
            public int Sex;
            public double Salary;
            public String FirstName;
            public String LastName;
        }
        class Program
        {
            [DllImport("Win32Native.dll")]<\/strong><\/font><\/p>\n

            public static extern int ModifyArrayOfEmployeeStruct(<\/strong><\/font><\/p>\n

                                                        int nSize,<\/strong><\/font><\/p>\n

                                                        [In, Out] Employee[] empArr);
            static void Main(string[] args)
            {
                int nCnt = 5; \/\/ Number of Items in Structure Array <\/strong><\/font><\/p>\n

                Employee[] emp = new Employee[nCnt];
                emp[0].FirstName = "Ramesh"; emp[0].LastName = "Sharma"; emp[0].Age = 42; emp[0].Salary = 40000; emp[0].Sex = 0;
                emp[1].FirstName = "Shalini"; emp[1].LastName = "Verma"; emp[1].Age = 30; emp[1].Salary = 25000; emp[1].Sex = 1;
                emp[2].FirstName = "Ramesh"; emp[2].LastName = "Sharma"; emp[2].Age = 51; emp[2].Salary = 35000; emp[2].Sex = 0;
                emp[3].FirstName = "Aarushi"; emp[3].LastName = "Shukla"; emp[3].Age = 25; emp[3].Salary = 20000; emp[3].Sex = 0;
                emp[4].FirstName = "Malini"; emp[4].LastName = "Kapoor"; emp[4].Age = 33; emp[4].Salary = 30000; emp[4].Sex = 1;<\/strong><\/font><\/p>\n

                Console.WriteLine("\\nEmployee Array Before Call");
    <\/strong><\/font>            for (int nI = 0; nI < nCnt; nI++)
                {
                    StringBuilder sb = new StringBuilder( "First Name=[" );
                    sb.Append(emp[nI].FirstName);
                    sb.Append("]  Last Name=[");
                    sb.Append(emp[nI].LastName );
                    sb.Append("]  Age=[");
                    sb.Append(emp[nI].Age .ToString ());
                    sb.Append("]  Salary=[");
                    sb.Append(emp[nI].Salary.ToString ("F2"));
                    sb.Append("]  Sex=[");
                    sb.Append(((emp[nI].Sex == 0) ? "Male" : "Female"));
                    sb.Append("]");
                    Console.WriteLine(sb.ToString ());
                }<\/strong><\/font><\/font><\/p>\n

                \/\/ Call the Function.<\/strong><\/font><\/p>\n

                ModifyArrayOfEmployeeStruct(emp.Length, emp);
    <\/strong><\/font><\/p>\n

                Console.WriteLine("\\nEmployee Array After Call");
                for (int nI = 0; nI < nCnt; nI++)
                {
                    StringBuilder sb = new StringBuilder("First Name=[");
                    sb.Append(emp[nI].FirstName);
                    sb.Append("]  Last Name=[");
                    sb.Append(emp[nI].LastName);
                    sb.Append("]  Age=[");
                    sb.Append(emp[nI].Age.ToString());
                    sb.Append("]  Salary=[");
                    sb.Append(emp[nI].Salary.ToString("F2"));
                    sb.Append("]  Sex=[");
                    sb.Append(((emp[nI].Sex == 0) ? "Male" : "Female"));
                    sb.Append("]");
                    Console.WriteLine(sb.ToString());
                }<\/strong><\/font><\/p>\n

            }
        }
    }
    <\/strong><\/font><\/p>\n

    <\/strong><\/p>\n

    <\/strong><\/p>\n

    Point of Interest<\/h4>\n<\/li>\n
  • namespace System.Runtime.InteropServices;<\/strong>  defines the declarations necessary for Interop operations, like DllImport<\/strong>, <\/li>\n
  • DllImport<\/strong> defines the DLL entry point.\n

    compile and execute you will get following output.<\/p>\n

    \"image\"<\/a><\/p>\n<\/li>\n","protected":false},"excerpt":{"rendered":"

    Let\u2019s assume you have a user defined structure \u201cEMPLOYEE\u201d in a win32 DLL (let say it \u201cWin32Native.dll\u201d) as shown below. typedef struct _EMPLOYEE {     int Age ;     int Sex;     double Salary ;     char* FirstName ;     char* LastName ; } EMPLOYEE; Define some functions in native dll (let say it \u201cWin32Native.dll\u201d) … Continue reading Modifying array of structures (default marshaling)<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3,9,15],"tags":[17,28],"class_list":["post-99","post","type-post","status-publish","format-standard","hentry","category-codeproject","category-interoperability","category-win32","tag-net","tag-marshaling","entry"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/posts\/99","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/comments?post=99"}],"version-history":[{"count":0,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/posts\/99\/revisions"}],"wp:attachment":[{"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=99"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=99"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/praveenkatiyar.in\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=99"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}