Windows System Programming Third Edition [Electronic resources] نسخه متنی

Figure 5-5 shows the relationship of the index file to the file to be sorted. Program 5-5, sortMM, is the main program that sets up the file mapping, sorts the index file, and displays the results. It calls a function, CreateIndexFile, which is shown in Program 5-6.

Program 5-5. sortMM: Based Pointers in an Index File

/* Chapter 5. sortMM command.
Memory Mapped sorting -- one file only. Options:
-r   Sort in reverse order.
-I   Use existing index file to produce sorted file. */
#include "EvryThng.h"
int KeyCompare (LPCTSTR , LPCTSTR);
DWORD CreateIndexFile (DWORD, LPCTSTR, LPTSTR);
DWORD KStart, KSize; /* Key start position & size (TCHAR). */
BOOL Revrs;
int _tmain (int argc, LPTSTR argv [])
{
HANDLE hInFile, hInMap; /* Input file handles. */
HANDLE hXFile, hXMap; /* Index file handles. */
HANDLE hStdOut = GetStdHandle (STD_OUTPUT_HANDLE);
BOOL IdxExists;
DWORD FsIn, FsX, RSize, iKey, nWrite, *pSizes;
LPTSTR pInFile = NULL;
LPBYTE pXFile = NULL, pX;
TCHAR _based (pInFile) *pIn;
TCHAR IdxFlNam [MAX_PATH], ChNewLine = TNEWLINE;
int FlIdx =
Options (argc, argv, _T ("rI"), &Revrs, &IdxExists, NULL);
/*   Step 1: Open and map the input file. */
hInFile = CreateFile (argv [FlIdx], GENERIC_READ | GENERIC_WRITE,
0, NULL, OPEN_EXISTING, 0, NULL);
hInMap = CreateFileMapping (hInFile, NULL,
PAGE_READWRITE, 0, 0, NULL);
pInFile = MapViewOfFile (hInMap, FILE_MAP_ALL_ACCESS, 0, 0, 0);
FsIn = GetFileSize (hInFile, NULL);
/* Steps 2 and 3: Create the index file name. */
_stprintf (IdxFlNam, _T ("%s%s"), argv [FlIdx], _T (".idx"));
if (!IdxExists)
RSize = CreateIndexFile (FsIn, IdxFlNam, pInFile);
/* Step 4: Map the index file. */
hXFile = CreateFile (IdxFlNam, GENERIC_READ | GENERIC_WRITE,
0, NULL, OPEN_EXISTING, 0, NULL);
hXMap = CreateFileMapping (hXFile, NULL, PAGE_READWRITE,
0, 0, NULL);
pXFile = MapViewOfFile (hXMap, FILE_MAP_ALL_ACCESS, 0, 0, 0);
FsX = GetFileSize (hXFile, NULL);
pSizes = (LPDWORD) pXFile; /* Size fields in .idx file. */
KSize = *pSizes; /* Key size */
KStart = *(pSizes + 1); /* Start position of key in record. */
FsX -= 2 * sizeof (DWORD);
/* Step 5: Sort the index file with qsort. */
if (!IdxExists)
qsort (pXFile + 2 * sizeof (DWORD), FsX / RSize,
RSize, KeyCompare);
/* Step 6: Output the input file in sorted order. */
pX = pXFile + 2 * sizeof (DWORD) + RSize - sizeof (LPTSTR);
for (iKey = 0; iKey < FsX / RSize; iKey++) {
WriteFile (hStdOut, &ChNewLine, TSIZE, &nWrite, NULL);
/*   The cast on pX is necessary! */
pIn = (TCHAR _based (pInFile)*) *(LPDWORD) pX;
while ((*pIn != CR || *(pIn + 1) != LF)
&& (DWORD) pIn < FsIn) {
WriteFile (hStdOut, pIn, TSIZE, &nWrite, NULL);
pIn++;
}
pX += RSize;
}
UnmapViewOfFile (pInFile);
CloseHandle (hInMap);
CloseHandle (hInFile);
UnmapViewOfFile (pXFile);
CloseHandle (hXMap);
CloseHandle (hXFile);
return 0;
}

Program 5-6 is the CreateIndexFile function, which creates the index file. It initially scans the input file to determine the key length from the first record.

Subsequently, it must scan the input file to find the bound of each varying-length record to set up the structure shown in Figure 5-5.

Program 5-6. sortMM: Creating the Index File

DWORD CreateIndexFile (DWORD FsIn, LPCTSTR IdxFlNam, LPTSTR pInFile)
{
HANDLE hXFile;
TCHAR _based (pInFile) *pInScan = 0;
DWORD nWrite;
/* Step 2a: Create an index file. Do not map it yet. */
hXFile = CreateFile (IdxFlNam, GENERIC_READ | GENERIC_WRITE,
FILE_SHARE_READ, NULL, CREATE_ALWAYS, 0, NULL);
/* Step 2b: Get first key & determine key size/start.
Skip white space and get key length. */
KStart = (DWORD) pInScan;
while (*pInScan != TSPACE && *pInScan != TAB)
pInScan++; /* Find the first key field. */
KSize = ((DWORD) pInScan - KStart) / TSIZE;
/* Step 3: Scan the complete file, writing keys
and record pointers to the key file. */
WriteFile (hXFile, &KSize, sizeof (DWORD), &nWrite, NULL);
WriteFile (hXFile, &KStart, sizeof (DWORD), &nWrite, NULL);
pInScan = 0;
while ((DWORD) pInScan < FsIn) {
WriteFile (hXFile, pInScan + KStart, KSize * TSIZE,
&nWrite, NULL);
WriteFile (hXFile, &pInScan, sizeof (LPTSTR),
&nWrite, NULL);
while ((DWORD) pInScan < FsIn && ((*pInScan != CR)
|| (*(pInScan + 1) != LF))) {
pInScan++; /* Skip to end of line. */
}
pInScan += 2; /* Skip past CR, LF. */
}
CloseHandle (hXFile);
/*   Size of an individual record. */
return KSize * TSIZE + sizeof (LPTSTR);
}