C++ for-loop logic: break after getting strings from cmdline arguments? - c++

Question

With the help of many people here, I've been writing a program that writes the contents of the Windows clipboard to a text file. (I'm working in Visual Studio 2010.) I've been trying to work out the logic of a for loop that will test the command-line arguments (if any); the arguments can be
a codepage number
a filename or path
or both, in any order. If no codepage is specified (or if the user specifies an invalid codepage), the program uses the default Windows codepage (typically 1252). If no filename is specified, the program writes the output to "#clip.txt".
I know my method of reading the arguments is inefficient, but it's the best I can figure out right now. I use two for loops. The first checks each command-line parameter; if the string is NOT all-digits, it uses the string as a filename and then breaks. The next loop again checks each parameter, and if the string is all-digits, it assigns it as the codepage number and then breaks.
The idea is that if the user enters
clipwrite 500 850
only the first (500) should get used as the codepage. And if the user enters
clipwrite foo.txt bar.txt
the output should be written to foo.txt.
My code seems to work correctly if the user enters no arguments, one argument only, or one number and one alpha string. But I'm clearly doing something wrong, because if the user enters
clipwrite 500 850
then 850 gets used (it should be ignored). And if the user enters
clipwrite foo.txt bar.txt
the program crashes. Can anyone help me sort what's wrong with my logic? Here's the relevant code (which uses a command-line parsing routine to get argc and argv):
if (argc > 1) {
// get name of output file if specified
for ( i = 1; i < argc; i++ ) {
if (i < 3) {
string argstr = argv[i];
//if string is not digits-only, use as filename
for (size_t n = 0; n <argstr.length(); n++) {
if (!isdigit( argstr[ n ]) ) {
OutFile = argv[i];
break;
}
}
}
}
// get codepage number if specified
for ( i = 1; i < argc; i++ ) {
if (i < 3) {
string argstr = argv[i];
for (size_t n = 0; n <argstr.length(); n++) {
if (!isdigit( argstr[ n ]) ) {
// if all chars are digits
} else {
// convert codepage string to integer
int cpint = atoi(argstr.c_str());
// check if codepage is valid; if so use it
if (IsValidCodePage(cpint)) {
codepage = "."+argstr;
}
break;
}
}
}
}
}
Many thanks for any help with this beginner-level problem.

Answer 1

Maybe something like this:
#include <iostream>
#include <string>
#include <cstring>
#include <cctype>
#include <cstdlib>
int main(int, char **argv) {
std::string filename = "#clip.txt";
int codepage = 1252;
bool bFilenameSet = false;
bool bCodepageSet = false;
for (++argv; *argv; ++argv) { // *argv == NULL at end of arguments
char *p = *argv;
for ( ; *p; ++p)
if (!isdigit(*p))
break;
if (*p) { // non-digit found
if (!bFilenameSet) {
filename = *argv;
bFilenameSet = true;
}
}
else {
if (!bCodepageSet) {
codepage = atoi(*argv);
bCodepageSet = true;
}
}
}
std::cout<< "Filename: "<< filename<< "\n";
std::cout<< "Codepage: "<< codepage<< "\n";
return 0;
}

Answer 2

I ran your program but it wasn't complete, so I assumed that isValidCodePage() function always returns true.
What I can see from your code is that you are overwriting codepage and Outfile because you are only breaking the inner loop, see this article for an explaination of the break statement

Answer 3

I don't see any immediate reason for a crash, but:
When issuing clipwrite 500 850 you use the codepage 850 since your break; only leaves the inner loop but your code keeps iterating over
the arguments and your codepage variable gets overwritten.
Your usage of isdigit is faulty. Whenever a string starts with a digit you try to interpret it as an integer even if its 1bla.txt.
atoi() is evil since it fails to report if a given string can't be parsed as a number. Better use std::stringstream and >> operator.
May be you should do it like this:
int cpint = -1;
std::string fname="";
for ( int i = 1; i < argc && i<3; i++ ) {
std::stringstream argss(argv[i]);
// Check if the string is a decimal
// and only a decimal
if( !(argss >> cpint) || !argss.eof()) {
fname=argv[i];
}
}
if(!fname.empty())
std::cerr << "filename '" << fname "'" << std::endl;
if(cpint!=-1)
std::cerr << "codepage: #" << cpint << std::endl;
Not really tested but I hope you get the idea

Answer 4

Using the answers here I finally got everything working, though I know my code is still inefficient. Here is the VS2010 source code that I used for this clipboard writing utility. Thanks to all who responded.
// ClipWrite.cpp
#include "stdafx.h"
#include <Windows.h>
#include <shellapi.h>
#include <iostream>
#include <fstream>
#include <codecvt> // for wstring_convert
#include <locale> // for codecvt_byname
#include <sstream>
using namespace std;
// helper gets path to this application
string ExePath() {
char buffer[MAX_PATH];
GetModuleFileNameA( NULL, buffer, MAX_PATH );
string::size_type pos = string( buffer ).find_last_of( "\\/" );
return string( buffer ).substr( 0, pos);
//return std::string( buffer ).substr( 0, pos);
}
// set variable for command-line arguments
char **argv = NULL;
// helper to get command-line arguments
int ParseCommandLine() {
int argc, BuffSize, i;
WCHAR *wcCommandLine;
LPWSTR *argw;
wcCommandLine = GetCommandLineW();
argw = CommandLineToArgvW( wcCommandLine, &argc);
argv = (char **)GlobalAlloc( LPTR, argc + 1);
for( i=0; i < argc; i++) {
BuffSize = WideCharToMultiByte( CP_ACP, WC_COMPOSITECHECK, argw[i], -1, NULL, 0, NULL, NULL );
argv[i] = (char *)GlobalAlloc( LPTR, BuffSize );
WideCharToMultiByte( CP_ACP, WC_COMPOSITECHECK, argw[i], BuffSize * sizeof( WCHAR ),argv[i], BuffSize, NULL, NULL );
}
return argc;
}
int CALLBACK WinMain(
_In_ HINSTANCE hInstance,
_In_ HINSTANCE hPrevInstance,
_In_ LPSTR lpCmdLine,
_In_ int nCmdShow)
{
// for logging in case of error
int writelog = 0;
string logtext = "";
// create output filename
string filename = ExePath() + "\\#clip.txt";
// get default codepage from Windows, typically 1252
int iCP=GetACP();
string sCP;
ostringstream convert;
convert << iCP;
sCP = convert.str();
// construct string to use for conversion routines (e.g. ".1252")
string sDefaultCP = "."+sCP;
string sOutputCP = "."+sCP;
// read command line for alternate codepage and/or filename
int i, argc;
argc = ParseCommandLine( );
if (argc > 1) {
bool bFilenameSet = false;
bool bCodepageSet = false;
int cpint = -1;
for ( i = 1; i < argc && i<3; i++ ) {
std::string argstr = argv[i];
//if string has only digits, use as codepage;
for (size_t n = 0; n <argstr.length(); n++) {
if (!isdigit( argstr[ n ]) ) {
if (!bFilenameSet) {
filename = argv[i];
bFilenameSet = true;
}
} else {
// convert codepage string to integer
if (!bCodepageSet) {
std::stringstream argss(argv[i]);
if( (argss >> cpint) || !argss.eof()) {
argstr = argv[i];
logtext = logtext + "Requested codepage (if any): " + argstr + "\n";
cout << "Requested codepage (if any): " << argstr << endl;
// check if codepage is valid; if so, use it
if (IsValidCodePage(cpint)) {
sCP = argstr;
sOutputCP = "."+argstr;
}
bCodepageSet = true;
}
}
}
}
}
}
cout << "Codepage used: " + sCP << endl;
// get clipboard text
string cliptext = "";
if (OpenClipboard(NULL)) {
if(IsClipboardFormatAvailable(CF_TEXT)) {
HGLOBAL hglb = GetClipboardData(CF_TEXT);
if (hglb != NULL) {
LPSTR lptstr = (LPSTR)GlobalLock(hglb);
if (lptstr != NULL) {
// read the contents of lptstr
cliptext = (char*)hglb;
// release the lock
GlobalUnlock(hglb);
}
}
}
CloseClipboard();
}
// create conversion routines
typedef std::codecvt_byname<wchar_t,char,std::mbstate_t> codecvt;
std::wstring_convert<codecvt> cp1252(new codecvt(sDefaultCP));
std::wstring_convert<codecvt> outpage(new codecvt(sOutputCP));
ofstream OutStream; // open an output stream
OutStream.open(filename, std::ios_base::binary | ios::out | ios::trunc);
// make sure file is successfully opened
if(!OutStream) {
writelog = 1;
logtext = logtext + "Error opening file " + filename + " for writing.\n";
//return 1;
} else {
// convert to DOS/Win codepage number in "outpage"
OutStream << outpage.to_bytes(cp1252.from_bytes(cliptext)).c_str();
OutStream.close(); // close output stream
if (writelog == 1) {
logtext = logtext + "Output file: " + filename + "\n";
}
}
if (writelog == 1) {
logtext = logtext + "Codepage used: " + sCP + "\n";
string LogFile = ExePath() + "\\#log.txt";
ofstream LogStream;
LogStream.open(LogFile, ios::out | ios::trunc);
if(!LogStream) {
cout << "Error opening file " << LogFile << " for writing.\n";
return 1;
}
LogStream << logtext;
LogStream.close(); // close output stream
}
return 0;
}