WIndow CreateFile ReadFile WriteFile - c

Question

I am a student so I apologize up front for not using the correct forum protocols. I am new to C, and really new to Win32 API. My assignment is to write a small C program that copies the contents of an existing file to a new file, using only Win32 I/O system calls: CreateFile(), ReadFile(), WriteFile(), etc... File names are to be specified on the command line. Right now I'm just trying to get the basics functions in place, I will then focus on error handling. This code compiles, creates a new file, but the data does not get copied to it. Any advice? thanks for taking a look!
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
int main(int argc, char *argv[])
{
char buff[4096];
DWORD dwBytesRead, dwBytesWritten;
DWORD dwBytesToWrite = (DWORD)strlen(buff);
//open source file and read it
HANDLE source;
// Create a handle for the source file
source=CreateFile(argv[1], GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
// Check for errors
if ( source == INVALID_HANDLE_VALUE ){
printf("Error, source file not opened.");
exit(EXIT_FAILURE);
}
else printf("The source file is %s\n", argv[1]);
//create a new file
HANDLE target;
target = CreateFile(argv[2], GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if ( target == INVALID_HANDLE_VALUE ){
printf("Error, target file not created.");
exit(EXIT_FAILURE);
}
else printf("The source file is %s\n", argv[2]);
//copy contents
ReadFile(source, buff, 4096, &dwBytesRead, NULL);
WriteFile(target, buff, dwBytesToWrite, &dwBytesWritten, NULL);
//copy complete
CloseHandle(source);
CloseHandle(target);
return 0;
}

Answer 1

As mentioned in comments, your code has a few mistakes in it. Try something more like this instead:
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
int main(int argc, char *argv[])
{
char buff[4096];
DWORD dwBytesRead, dwBytesWritten;
// Open the source file
HANDLE source = CreateFileA(argv[1], GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
// Check for error
if (source == INVALID_HANDLE_VALUE) {
printf("Source file not opened. Error %u", GetLastError());
return EXIT_FAILURE;
}
printf("The source file is %s\n", argv[1]);
// Create a new file
HANDLE target = CreateFileA(argv[2], GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
// Check for error
if (target == INVALID_HANDLE_VALUE) {
printf("Target file not created. Error %u", GetLastError());
CloseHandle(source);
return EXIT_FAILURE;
}
printf("The target file is %s\n", argv[2]);
// Copy contents
bool ok = true;
do {
// Read file, check for error
if (!ReadFile(source, buff, sizeof(buff), &dwBytesRead, NULL)) {
printf("Source file not read from. Error %u", GetLastError());
ok = false;
break;
}
// Check for EOF reached
if (dwBytesRead == 0) {
break;
}
// Write file, check for error
if (!WriteFile(target, buff, dwBytesRead, &dwBytesWritten, NULL)) {
printf("Target file not written to. Error %u", GetLastError());
ok = false;
break;
}
}
while (true);
// Copy complete
CloseHandle(source);
CloseHandle(target);
// Check for error
if (!ok) {
DeleteFileA(argv[2]);
return EXIT_FAILURE;
}
// all OK
return 0;
}