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I have been trying to find the length of string which has an array of chars with strlen() function but it is not working. The code I am using is something like this:

string s[]={"a","b","c"};
int len = strlen(s.c_str());

It produces the following error:

"request for member âc_strâ in âwArrayâ, which is of non-class type"

But when I have used this strlen() function on strings before like this, it worked fine:

fin.open("input.txt");
string tempStr;
getline(fin, tempStr,'\n');
int len = strlen(tempStr.c_str());

What I am missing here? I know I can find the length of string s[] with 

int size = sizeof( s ) / sizeof( s[ 0 ] );

But why can't I use strlen(). Can someone explain what is going on?

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  • 3
    s is an array, it has no c_str function. is std::vector an option? Commented Feb 17, 2013 at 8:25
  • You are missing the fact that std::string is not std::string[]. Commented Feb 17, 2013 at 8:27
  • @Billz But it works for char type array....???????????/ Commented Feb 17, 2013 at 8:29
  • @n.m. Then why does it work on tempStr. That is a string as well. Commented Feb 17, 2013 at 8:31
  • 1
    a string is different from an array of strings. Commented Feb 17, 2013 at 8:32

4 Answers 4

Reset to default
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Finding the length of a fixed size array of any type is easy enough with a helper function template:

#include <cstddef> // for std::size_t

template< class T, size_t N >
std::size_t length(const T (&)[N] )
{
  return N;
};

string s[]={"a","b","c"};
std::cout << length(s) << std::endl;

In C++11, the function would be constexpr.

Concerning strlen, it counts chars until it finds a null termination character \0. When you call std::string'sc_str() method, you get a pointer to the first char in a null terminated string.

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3 Comments

@juanchopanza Thanks.. But i really need to know why strlen() works on tempStr and not string s. (see code for tempStr and s)
@AlexChamberlain I didn't remember off the top of my head which header is required for std::size_t. Fixed now.
@DeadCoder I added something about strlen.
1

A C++ way to do it would be using std::vector

vector<string> ss;

ss.push_back("a");
ss.push_back("b");
ss.push_back("c");

cout << ss.size(); // number of strings in your vector : 3

you can also access each string :

cout << ss[0].size(); // 1
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0

it must be like :

string s[]={"a","b","c"};  //array of string
for(auto i:s){
int len = strlen(i.c_str());  because you need to convert one string to c type string
cout<<len<<" ";
}

to get the array length :

std::array<int> nums {1, 3, 5, 7};

std::cout << "nums contains " << nums.size() << " elements.\n";

http://en.cppreference.com/w/cpp/container/array/size

strlen() accepts ctype strings. and c_str() convert the string(STL) to ctype string(Null terminated) which is accepted by strlen.

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7 Comments

@Arpit of course it is 1, Every element of the array has length 1.
so this is what to be expected.
@juanchopanza we understand the ques. differently . you work on array and i work on individual string.
Sorry, that comment was meant to be for @DeadCoder.
@juanchopanza Just last thing. What is difference between ctype string and string ????
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0

the define of strlen: size_t strlen ( const char * str ), note the type of input parameter. you define string s[]={"a","b","c"}; which is an array, so the following statement will work: strlen(s[0].c_str()); In addition, to calculate the length of array s, sizeof( s ) / sizeof( s[ 0 ] ) work only when every element of 's' has the same length.

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