how to find number of elements in an array of strings in c++?

i have an array of string.

std::string str[10] = {"one","two"}

How to find how many strings are present inside the str[] 开发者_JAVA百科array?? Is there any standard function?

---

There are ten strings in there despite the fact that you have only initialised two of them:

#include <iostream>
int main (void) {
    std::string str[10] = {"one","two"};
    std::cout << sizeof(str)/sizeof(*str) << std::endl;
    std::cout << str[0] << std::endl;
    std::cout << str[1] << std::endl;
    std::cout << str[2] << std::endl;
    std::cout << "===" << std::endl;
    return 0;
}

The output is:

10
one
two

===

If you want to count the non-empty strings:

#include <iostream>
int main (void) {
    std::string str[10] = {"one","two"};
    size_t count = 0;
    for (size_t i = 0; i < sizeof(str)/sizeof(*str); i++)
        if (str[i] != "")
            count++;
    std::cout << count << std::endl;
    return 0;
}

This outputs 2 as expected.

---

If you want to count all elements sizeof technique will work as others pointed out. If you want to count all non-empty strings, this is one possible way by using the standard count_if function.

bool IsNotEmpty( const std::string& str )
{
    return !str.empty();
}


int main ()
{
    std::string str[10] = {"one","two"};

    int result = std::count_if(str, &str[10], IsNotEmpty);
    cout << result << endl; // it will print "2"

    return 0;
 }

---

I don't know that I would use an array of std::strings. If you're already using the STL, why not consider a vector or list? At least that way you could just figure it out with std::vector::size() instead of working ugly sizeof magic. Also, that sizeof magic won't work if the array is stored on the heap rather than the stack.

Just do this:

std::vector<std::string> strings(10);
strings[0] = "one";
strings[1] = "two";

std::cout << "Length = " << strings.size() << std::endl;

---

You can always use countof macro to get the number of elements, but again, the memory was allocated for 10 elements and thats the count that you'll get.

---

The ideal way to do this is

std::string str[] = {"one","two"}

int num_of_elements = sizeof( str ) / sizeof( str[ 0 ] );

---

Since you know the size. You could do a binary search for not null/empty.

str[9] is empty
str[5] is empty
str[3] is not empty
str[4] is empty
You have 4 items.

I don't really feel like implementing the code, but this would be quite quick.

---

Simply use this function for 1D string array:

template<typename String, uint SIZE>  // String can be 'string' or 'const string'
unsigned int NoOfStrings (String (&arr)[SIZE])
{
  unsigned int count = 0;
  while(count < SIZE && arr[count] != "")
    count ++;
  return count;
}

Usage:

std::string s1 = {"abc", "def" };
int i = NoOfStrings(s1);  // i = 2

I am just wondering if we can write a template meta program for this ! (since everything is known at compile time)

---

A simple way to do this is to use the empty() member function of std::string like this e.g.:

    size_t stringArrSize(std::string *stringArray) {

       size_t num = 0;
       while (stringArray->empty() != true) {
           ++num;
           stringArray++;
       }
       return num;

    }