How do I convert argv to lpCommandLine parameter of CreateProcess? - c++

Question

Let I want to write an application, that launches another application. Like this:
# This will launch another_app.exe
my_app.exe another_app.exe
# This will launch another_app.exe with arg1, arg and arg3 arguments
my_app.exe another_app.exe arg1 arg2 arg3
The problem here is that I'm getting char* argv[] in my main function, but I need to merge it to LPTSTR in order to pass it to CreateProcess.
There is a GetCommandLine function, but I cannot use it because I'm porting code from Linux and tied to argc/argv (otherwise, it's a very ugly hack for me).
I cannot easily merge arguments by hand, because argv[i] might contain spaces.
Basically, I want the reverse of CommandLineToArgvW. Is there a standard way to do this?

Answer 1

The definitive answer on how to quote arguments is on Daniel Colascione's blog:
https://blogs.msdn.microsoft.com/twistylittlepassagesallalike/2011/04/23/everyone-quotes-command-line-arguments-the-wrong-way/
I am reluctant to quote the code here because I don't know the license. The basic idea is:
for each single argument:
if it does not contain \t\n\v\",
just use as is
else
output "
for each character
backslashes = 0
if character is backslash
count how many successive backslashes there are
fi
if eow
output the backslashs doubled
break
else if char is "
output the backslashs doubled
output \"
else
output the backslashes (*not* doubled)
output character
fi
rof
output "
fi // needs quoting
rof // each argument
If you need to pass the command line to cmd.exe, see the article (it's different).
I think it is crazy that the Microsoft C runtime library doesn't have a function to do this.

Answer 2

There is no Win32 API that does the reverse of CommandLineToArgvW(). You have to format the command line string yourself. This is nothing more than basic string concatenation.
Microsoft documents the format for command-line arguments (or at least the format expected by VC++-written apps, anyway):
Parsing C++ Command-Line Arguments
Microsoft C/C++ startup code uses the following rules when
interpreting arguments given on the operating system command line:
Arguments are delimited by white space, which is either a space or a
tab.
The caret character (^) is not recognized as an escape character or
delimiter. The character is handled completely by the command-line
parser in the operating system before being passed to the argv array
in the program.
A string surrounded by double quotation marks ("string") is
interpreted as a single argument, regardless of white space contained
within. A quoted string can be embedded in an argument.
A double quotation mark preceded by a backslash (\") is interpreted
as a literal double quotation mark character (").
Backslashes are interpreted literally, unless they immediately
precede a double quotation mark.
If an even number of backslashes is followed by a double quotation
mark, one backslash is placed in the argv array for every pair of
backslashes, and the double quotation mark is interpreted as a string
delimiter.
If an odd number of backslashes is followed by a double quotation
mark, one backslash is placed in the argv array for every pair of
backslashes, and the double quotation mark is "escaped" by the
remaining backslash, causing a literal double quotation mark (") to be
placed in argv.
It should not be hard for you to write a function that takes an array of strings and concatenates them together, applying the reverse of the above rules to each string in the array.

Answer 3

You need to recreate the command line, taking care of having all program name and arguments enclosed in ". This is done by concatenating a \" to these strings, one at the beginning, one at the end.
Assuming the program name to be created is argv[1], the first argument argv[2] etc...
char command[1024]; // size to be adjusted
int i;
for (*command=0, i=1 ; i<argc ; i++) {
if (i > 1) strcat(command, " ");
strcat(command, "\"");
strcat(command, argv[i]);
strcat(command, "\"");
}
Use the 2nd argument of CreateProcess
CreateProcess(NULL, command, ...);

Answer 4

You can check out the below code if it suits your need, the txt array sz can be used as a string pointer. I have added code support for both Unicode and MBCS,
#include <string>
#include <vector>
#ifdef _UNICODE
#define String std::wstring
#else
#define String std::string
#endif
int _tmain(int argc, _TCHAR* argv[])
{
TCHAR sz[1024] = {0};
std::vector<String> allArgs(argv, argv + argc);
for(unsigned i=1; i < allArgs.size(); i++)
{
TCHAR* ptr = (TCHAR*)allArgs[i].c_str();
_stprintf_s(sz, sizeof(sz), _T("%s %s"), sz, ptr);
}
return 0;
}