Argument Definitions
The arguments in the prototype
int main( int argc[ , char *argv[ ] [, char *envp[ ] ] ] );
int wmain( int argc[ , wchar_t *argv[ ] [, wchar_t *envp[ ] ] ] );
allow convenient command-line parsing of arguments and, optionally, access to environment variables. The argument definitions are as follows:
argc
An integer that contains the count of arguments that follow in argv. The argc parameter is always greater than or equal to 1.argv
An array of null-terminated strings representing command-line arguments entered by the user of the program. By convention, argv**[0]** is the command with which the program is invoked, argv**[1]** is the first command-line argument, and so on, until argv**[argc]**, which is always NULL. See Customizing Command Line Processing for information on suppressing command-line processing.The first command-line argument is always argv**[1]** and the last one is argv**[argc – 1]**.
Note
By convention, argv[0] is the command with which the program is invoked. However, it is possible to spawn a process using CreateProcess and if you use both the first and second arguments (lpApplicationName and lpCommandLine), argv[0] may not be the executable name; use GetModuleFileName to retrieve the executable name, and its fully-qualified path.
Microsoft Specific
- envp
The envp array, which is a common extension in many UNIX systems, is used in Microsoft C++. It is an array of strings representing the variables set in the user's environment. This array is terminated by a NULL entry. It can be declared as an array of pointers to char (char *envp[ ]) or as a pointer to pointers to char (char **envp**). If your program uses wmain instead of main, use the wchar_t data type instead of char. The environment block passed to main and wmain is a "frozen" copy of the current environment. If you subsequently change the environment via a call to putenv or _wputenv, the current environment (as returned by getenv/_wgetenv** and the _environ/ _wenviron variable) will change, but the block pointed to by envp will not change. See Customizing Command Line Processing for information on suppressing environment processing. This argument is ANSI compatible in C, but not in C++.
Example
The following example shows how to use the argc, argv, and envp arguments to main:
// argument_definitions.cpp
// compile with: /EHsc
#include <iostream>
#include <string.h>
using namespace std;
int main( int argc, char *argv[], char *envp[] ) {
int iNumberLines = 0; // Default is no line numbers.
// If /n is passed to the .exe, display numbered listing
// of environment variables.
if ( (argc == 2) && _stricmp( argv[1], "/n" ) == 0 )
iNumberLines = 1;
// Walk through list of strings until a NULL is encountered.
for( int i = 0; envp[i] != NULL; ++i ) {
if( iNumberLines )
cout << i << ": " << envp[i] << "\n";
}
}