a_env.c

C标准库源代码

/***
*a_env.c - A version of GetEnvironmentStrings.
*
*       Copyright (c) 1993-1997, Microsoft Corporation.  All rights reserved.
*
*Purpose:
*       Use GetEnvironmentStringsW if available, otherwise use A version.
*
*******************************************************************************/

#include <cruntime.h>
#include <internal.h>
#include <stdlib.h>
#include <setlocal.h>
#include <awint.h>
#include <dbgint.h>

#define USE_W   1
#define USE_A   2

/***
*LPVOID __cdecl __crtGetEnvironmentStringsA - Get normal environment block
*
*Purpose:
*       Internal support function. Since GetEnvironmentStrings returns in OEM
*       and we want ANSI (note that GetEnvironmentVariable returns ANSI!) and
*       SetFileApistoAnsi() does not affect it, we have no choice but to
*       obtain the block in wide character and convert to ANSI.
*
*Entry:
*       VOID
*
*Exit:
*       LPVOID - pointer to environment block
*
*Exceptions:
*
*******************************************************************************/

LPVOID __cdecl __crtGetEnvironmentStringsA(
        VOID
        )
{
        static int f_use = 0;
        wchar_t *wEnv = NULL;
        wchar_t *wTmp;
        char *aEnv = NULL;
        char *aTmp;
        int nSizeW;
        int nSizeA;

        /*
         * Look for 'preferred' flavor. Otherwise use available flavor.
         * Must actually call the function to ensure it's not a stub.
         */

        if ( 0 == f_use )
        {
            if ( NULL != (wEnv = GetEnvironmentStringsW()) )
                f_use = USE_W;

            else if ( NULL != (aEnv = GetEnvironmentStringsA()) )
                f_use = USE_A;

            else
                return NULL;
        }

        /* Use "W" version */

        if (USE_W == f_use)
        {
            /* obtain wide environment block */
            if ( NULL == wEnv )
                if ( NULL == (wEnv = GetEnvironmentStringsW()) )
                    return NULL;

            /* look for double null that indicates end of block */
            wTmp = wEnv;
            while ( *wTmp != L'\0' ) {
                if ( *++wTmp == L'\0' )
                    wTmp++;
            }

            /* calculate total size of block, including all nulls */
            nSizeW = wTmp - wEnv + 1;

            /* find out how much space needed for multi-byte environment */
            nSizeA = WideCharToMultiByte(   CP_ACP,
                                            0,
                                            wEnv,
                                            nSizeW,
                                            NULL,
                                            0,
                                            NULL,
                                            NULL );

            /* allocate space for multi-byte string */
            if ( (nSizeA == 0) ||
                 ((aEnv = (char *)_malloc_crt(nSizeA)) == NULL) )
            {
                FreeEnvironmentStringsW( wEnv );
                return NULL;
            }

            /* do the conversion */
            if ( !WideCharToMultiByte(  CP_ACP,
                                        0,
                                        wEnv,
                                        nSizeW,
                                        aEnv,
                                        nSizeA,
                                        NULL,
                                        NULL ) )
            {
                _free_crt( aEnv );
                aEnv = NULL;
            }

            FreeEnvironmentStringsW( wEnv );
            return aEnv;
        }

        /* Use "A" version */

        if ( USE_A == f_use )
        {
            if ( NULL == aEnv )
                if ( NULL == (aEnv = GetEnvironmentStringsA()) )
                    return NULL;

            /* determine how big a buffer is needed */

            aTmp = aEnv;

            while ( *aTmp != '\0' ) {
                if ( *++aTmp == '\0' )
                    aTmp++;
            }

            nSizeA = aTmp - aEnv + 1;

            if ( NULL == (aTmp = _malloc_crt( nSizeA )) ) {
                FreeEnvironmentStringsA( aEnv );
                return NULL;
            }

            memcpy( aTmp, aEnv, nSizeA );

            FreeEnvironmentStringsA( aEnv );

            return aTmp;
        }

        return NULL;
}