function to find length of 2d string array in cpp?

Question

Is there any inbuilt function in cpp that can give me the length of a 2d char array

for ex, the function for args

const char* args[] = {"412", "..7", ".58", "7.8", "32.", "6..", "351", "3.9", "985", "...", ".46"}

should return 11

There is no actual function, since using an array as a function parameter causes it to decay to a pointer. The macros given in the answers can be used in the array's scope. — David Thornley
– David Thornley, Commented Feb 9, 2012 at 22:19
If you want to do something like that in an idiomatic C++ program, it's more like std::vector<std::string> rather than a char *args[]. That way, you do get functions that work. — David Thornley
– David Thornley, Commented Feb 9, 2012 at 22:21
Even though the question is narrowly focused on 2d string array, the answer by R. Martinho Fernandes has much wider application to arrays in general. How about editing the title to ask the general question "Function to find length of array in C++?" so the question can be voted up and get more exposure? — Mark Taylor
– Mark Taylor, Commented Feb 10, 2012 at 4:55

R. Martinho Fernandes · Accepted Answer · 2012-02-09 22:19:37Z

7

I like to use a template function for this.

template <typename T, std::size_t N>
std::size_t size(T(&)[N]) { return N; }

The advantage over an approach using sizeof is that you can't accidentally do it with a pointer.

answered Feb 9, 2012 at 22:19

community wiki

R. Martinho Fernandes

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3 Comments

Michael Dorgan Over a year ago

Bah, you and your fancy template stuff :)

Robᵩ Over a year ago

+1 Specifically, this version fails to compile when passed a pointer. The alternative, sizeof A/sizeof A[0], returns the wrong number when passed a pointer. Failing to compile is always better than giving the wrong answer.

rohanag Over a year ago

I tried sizeof(args)/sizeof(args[0]); and it works :) I didn't want to go for templates, I don't know how to Initialize a 2d string array in them.

hmjd · Accepted Answer · 2012-02-09 22:18:11Z

4

This will give the number of elements in args:

sizeof(args) / sizeof(args[0])

answered Feb 9, 2012 at 22:18

hmjd

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1 Comment

Keith Over a year ago

And I'd note that even if you go for one of the other new-fangled ways listed, you should remember this idiom as you'll come across it in a ton of old C++ and C code.

Blaisorblade · Accepted Answer · 2012-02-10 13:48:49Z

2

In C++11 you can use:

std::end(args) - std::begin(args)

edited Feb 10, 2012 at 13:48

Blaisorblade

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answered Feb 9, 2012 at 22:26

Robᵩ

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Comments

Michael Dorgan · Accepted Answer · 2012-02-09 22:17:12Z

1

sizeof(args) / sizeof(*args)

answered Feb 9, 2012 at 22:17

Michael Dorgan

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