How to read cstrings from char**?

Question

I have a char** (a null terminate array: last element of array is NULL) returned by a function (which I can not change):

char** ptar = get_ptar();

I want to iterate over it and pass its value to another function (again which I can not change):

collection(int index, char* str);

I have this code so far:

int I = 0;
while (*ptar != 0) 
{
  collection(i, (char*)(ptar));
  ptar++; i++;
}

But it passes garbage value.

Is there a better approach get string out of a null-terminated array?

Related question:

Is there a way to get the length of char** ptar using C++11's:

std::char_traits<?>::length

Don't use C-style casts, use C++ casts. If you use a cast other than static_cast, something is probably (but not always) wrong. In this case, you would see that `static_cast(ptar)` does not compile, and this is your hint that something is wrong. — Neil Kirk, Nov 16 '14 at 18:55
@Neil Kirk, Thanks for the tips. I am avoiding casting, it is just a middle tier where I need to pipe `char*`s to another function. — Annie, Nov 16 '14 at 19:30

Vlad from Moscow · Accepted Answer · 2014-11-16T19:07:33.853

4

Try the following:

for ( int i = 0; *( ptar + i ) != 0; i++ ) 
{
  collection( i, *( ptar + i ) );
}

Or

for ( int i = 0; ptar[i] != 0; i++ ) 
{
  collection( i, ptar[i] );
}

In C++ 2011 instead of integral constant 0 as null pointer expression you may use nullptr

To find the length of ptar you can do this:

int n = 0;

while ( ptar[n] ) ++n;

edited Nov 16 '14 at 19:07

answered Nov 16 '14 at 18:57

Vlad from Moscow

1 Answers1