How do I convert argv to lpCommandLine parameter of CreateProcess?

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

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 2

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 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 2 ^nd 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;
            }