lesson3

_posts/2024-01-28-lesson3.md

@@ -14,7 +14,96 @@ permalink: /lesson3/
 <details>
 <summary>Click to see C implementation</summary>
 
-[C implementation will go here]
+```c
+#include <windows.h>
+#include <stdio.h>
+#include <tchar.h>
+
+#define BUF_SIZE 512 // (1) BUF_SIZE macro definition: preprocessor replaces with 
+                     // literal 512 (0x200 in hex). Compiler allocates no memory;
+                     // simply substitutes. Impacts stack buffer size in CatFile.
+                     // 512 chosen as a common I/O buffer size.
+
+static void CatFile(HANDLE hIn, HANDLE hOut);
+static void ReportError(LPCTSTR msg, DWORD errCode, BOOL showErrMsg);
+
+int _tmain(int argc, TCHAR* argv[]) {
+    HANDLE hIn, hStdIn = GetStdHandle(STD_INPUT_HANDLE);
+    HANDLE hStdOut = GetStdHandle(STD_OUTPUT_HANDLE);
+    BOOL dashS = FALSE;
+    int iFirstFile = 1;
+
+    /* Flow Step 1a: Parse Options */
+    for (int i = 1; i < argc; i++) {
+        if (_tcscmp(argv[i], _T("-s")) == 0) {
+            dashS = TRUE;
+            iFirstFile++;
+        }
+        else if (argv[i][0] == _T('-')) {
+            iFirstFile++;
+        }
+        else {
+            break;
+        }
+    }
+
+    /* Flow Step 2: Input Source Decision */
+    if (iFirstFile >= argc) {
+        CatFile(hStdIn, hStdOut);
+        return 0;
+    }
+
+    /* Flow Step 3: File Processing Loop */
+    for (int i = iFirstFile; i < argc; i++) {
+        hIn = CreateFile(argv[i], GENERIC_READ, 0, NULL,
+            OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+
+        if (hIn == INVALID_HANDLE_VALUE) {
+            if (!dashS) 
+                ReportError(_T("File open error"), GetLastError(), TRUE);
+            continue;
+        }
+
+        CatFile(hIn, hStdOut);
+
+        DWORD err = GetLastError();
+        if (err != 0 && !dashS) {
+            ReportError(_T("Processing error"), err, TRUE);
+        }
+
+        CloseHandle(hIn);
+    }
+    return 0;
+}
+
+static void CatFile(HANDLE hIn, HANDLE hOut) {
+    BYTE buffer[BUF_SIZE];
+    DWORD nRead, nWritten;
+
+    while (ReadFile(hIn, buffer, BUF_SIZE, &nRead, NULL) && nRead > 0) {
+        if (!WriteFile(hOut, buffer, nRead, &nWritten, NULL) 
+            || nWritten != nRead) {
+            break;
+        }
+    }
+}
+
+static void ReportError(LPCTSTR msg, DWORD errCode, BOOL showErrMsg) {
+    _ftprintf(stderr, _T("ERROR: %s"), msg);
+
+    if (showErrMsg) {
+        LPVOID errMsg;
+        FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
+            FORMAT_MESSAGE_FROM_SYSTEM,
+            NULL, errCode, 0,
+            (LPTSTR)&errMsg, 0, NULL);
+
+        _ftprintf(stderr, _T(" (%s)"), (LPTSTR)errMsg);
+        LocalFree(errMsg);
+    }
+    _ftprintf(stderr, _T("\n"));
+}
+```
 
 </details>