result of passing argv variable to main in this format main( int argc, char const * argv )

Question

I am trying to figure out what will be result of passing argv variable to main in this format. main( int argc, char const * argv ).

I know right way of using it is main( int argc, char const **argv) or main( int argc, char const *argv[]).

Here is my code snippet,

#include <stdio.h> int main( int argc, char const * argv ) { for( int i = 0; i < argc; ++i ) { printf("%s\n", argv[i]); } }

Here is output,

$ ./a.exe

..

$ ./a.exe 1

2

....

$ ./a.exe 1 2

2

...

Does it fetch from whatever, argv points? Why does it terminate before even reaching argc.

It's actually not the right way unless your implementation allows it. The C standard only specifies argv as a buffer of pointers to non-const strings. — StoryTeller - Unslander Monica
– StoryTeller - Unslander Monica, Commented Mar 21, 2017 at 16:31
In your code as written, argv[i] will be a char value. In the printf call, that will be promoted to an int value. However, the printf function is expecting a valid pointer to a null-terminated sequence of char at that position, not some bogus pointer value. — Ian Abbott
– Ian Abbott, Commented Mar 21, 2017 at 19:14

Sourav Ghosh · Accepted Answer · 2017-03-21 16:40:13Z

It causes undefined behavior as the supplied type and the expected type does not match thereby this is a clear case of constraint violation.

Quoting C11, chapter chapter §5.1.2.2.1/p2, (emphasis mine)

If they are declared, the parameters to the main function shall obey the following constraints:

...

If the value of argc is greater than zero, the array members argv[0] through argv[argc-1] inclusive shall contain pointers to strings, which are given implementation-defined values by the host environment prior to program startup

You can re-write char * argv[] as char **argv ^NOTE considering the array decay property, but a char *[] and a char * are not compatible in any way.

NOTE:

Quoting C11, chapter §5.1.2.2.1, footnote 10)

Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as char ** argv, and so on.

Additionally, the printf call has undefined behavior because the types of the arguments differ from those specified by the format specifier string.

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