In command line arguments in C we can specify the arguments vector as char *argv[] or char **argv i understand the first one which is an array of pointers to characters but what is the relationship between an array of pointers to characters and the second type which looks a pointer to pointer to character?

CodePudding user response：

The difference between char *argv[] and char **argv is that:

• char *argv[] is a array of char * pointers.

• char **argv is a pointer to another pointer which points to a char.

char *argv[] can be visualized like this:

p1 -> "hello"   
p2 -> "world"  
p3 -> "!"

// p1, p2 and p3 are 
// pointers to strings
// they have type char *
 _________________
 |  p1| p2 | p3  |     
 —————————————————
// argv looks like this
// it is an array of all the pointers

when referencing the name of the array argv in an expression it will yield a pointer to the first element in the array.

The type of the array name argv when used in an expression is char **. This is because:

• The array name argv decays to a pointer to the first element of the array.

• The first element also happens to be a pointer, so argv is essentially a pointer to another pointer hence the type is char **

CodePudding user response：

Function parameters that are arrays get implicitly adjusted by the compiler into a pointer to the first item of that array.

In case of the array char* argv[], it's an array of char* and a pointer to the first item is therefore a char**. Therefore it doesn't matter if you type char* argv[]or char**, they are equivalent in this specific case.

Also since the char* [] will get adjusted to char**, the size of the array doesn't matter. You could write char* argv [42] and that would be equivalent as well.

Subjectively, char* argv[] could be regarded as the most correct form, since it is 1) self-documenting - we are dealing with an array - and 2) the form used in the C standard 5.1.2.2.1 (hosted systems).