Maximum Length of Command Line String

As @Sugrue I'm also digging out an old thread.

To explain why there is 32768 (I think it should be 32767, but lets believe experimental testing result) characters limitation we need to dig into Windows API.

No matter how you launch program with command line arguments it goes to ShellExecute, CreateProcess or any extended their version. These APIs basically wrap other NT level API that are not officially documented. As far as I know these calls wrap NtCreateProcess, which requires OBJECT_ATTRIBUTES structure as a parameter, to create that structure InitializeObjectAttributes is used. In this place we see UNICODE_STRING. So now lets take a look into this structure:

typedef struct _UNICODE_STRING {
    USHORT Length;
    USHORT MaximumLength;
    PWSTR  Buffer;
} UNICODE_STRING;

It uses USHORT (16-bit length [0; 65535]) variable to store length. And according this, length indicates size in bytes, not characters. So we have: 65535 / 2 = 32767 (because WCHAR is 2 bytes long).

There are a few steps to dig into this number, but I hope it is clear.

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Also, to support @sunetos answer what is accepted. 8191 is a maximum number allowed to be entered into cmd.exe, if you exceed this limit, The input line is too long. error is generated. So, answer is correct despite the fact that cmd.exe is not the only way to pass arguments for new process.

Sorry for digging out an old thread, but I think sunetos' answer isn't correct (or isn't the full answer). I've done some experiments (using ProcessStartInfo in c#) and it seems that the 'arguments' string for a commandline command is limited to 2048 characters in XP and 32768 characters in Win7. I'm not sure what the 8191 limit refers to, but I haven't found any evidence of it yet.

From the Microsoft documentation: Command prompt (Cmd. exe) command-line string limitation

On computers running Microsoft Windows XP or later, the maximum length of the string that you can use at the command prompt is 8191 characters.