CODEWITHSUNDEEP
c++char
samprat
samprat

Reputation: 2214

how to find length of char array containing zeros as elements

wondering how would I find the length of char array . for example

char buffer[20];
buffer[0] = 0x01;
buffer[1] = 0x02;
buffer[3] = 0x00;
buffer[4] = 0x04;
buffer[5] = 0x01;
buffer[6] = 0x02;
buffer[7] = 0x00;
buffer[8] = 0x04;

std::cout << "the len of array = "<< strlen(buffer) << std::endl;

o/p = the len of array = 3

expected o/p = 8

NOw issue is zeros can occur anywhere in the array of character elements.and I need true len i.e 8

Upvotes: 1

Views: 935

Answers (3)

R Sahu
R Sahu

Reputation: 206647

When you have an array, you can use sizeof to get the total memory used by the array.

char buffer[20];
// 
// ...
//

size_t size = sizeof(buffer); // This gives you total memory needed to hold buffer.
size_t length = sizeof(buffer)/sizeof(char); // In this case size and length will be
                                             // same since sizeof(char) is 1.

If you have an array of other types,

int buffer[20];
// 
// ...
//

size_t size = sizeof(buffer); // This gives you total memory needed to hold buffer.
size_t length = sizeof(buffer)/sizeof(int); // The length of the array.

There are pitfalls to be aware of using sizeof to get the memory used by an array. If you pass buffer to a function, you lose the ability to compute the length of the array.

void foo(char* buffer)
{
   size_t size = sizeof(buffer); // This gives you the size of the pointer
                                 // not the size of the array.
}

void bar()
{
   char buffer[20];

   // sizeof(buffer) is 20 here. But not in foo.

   foo(buffer);
}

If you need to be able to compute the length of the array at all times, std::vector<char> and std::string are better choices.

void foo(std::vector<char>& buffer)
{
   size_t size = buffer.size() // size is 20 after call from bar.
}

void bar()
{
   std::vector<char> buffer(20);
   size_t size = buffer.size() // size is 20.

   foo(buffer);
}

Upvotes: 0

Roddy
Roddy

Reputation: 68053

In C++ you would use a std::vector<char> or a std::string. Both store the length independently of the data so can hold zeros in them.

Beware that 'c' style literal strings are always zero terminated, so the following code gives you an empty string because the NUL terminates the string construction early.

std:string foo("\0Hello, world!");

Upvotes: 1

Chris Dodd
Chris Dodd

Reputation: 126328

Arrays in C (or C++) don't keep track of how much data has been stored in them. If you want to know the size of the stored data (as opposed to the size of the array), you'll need to track that yourself in another variable, or use a sentinel (such as NULL) that marks the end of the stored data.

Alternately, since you appear to be using C++ (despite the C tag), you can use a std::vector or std::string which tracks the size for you.

Upvotes: 3

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