Component bdlb_cstringless [Package bdlb]

Provide a standard compatible less-than predicate for C-strings. More...

Namespaces
namespace	bdlb

---

Detailed Description

Outline

• Purpose
• Classes
• Description
  • Usage
    • Example 1: Basic Use of bdlb::CStringLess

Purpose:

Provide a standard compatible less-than predicate for C-strings.

Classes:

bdlb::CStringLess

a standard compatible less-than predicate for C-strings.

See also:

bsl_map, bsl_set

Description:

This component provides a struct, bdlb::CStringLess, that defines a functor that compares two null-terminated strings using a case-sensitive string comparison, rather than simply comparing the two addresses (as the std::less functor would do). This lexicographical ordering makes CStringLess suitable for supporting C-strings as keys in associative containers. Note that the container behavior would be undefined if the strings referenced by such pointers were to change value.

Usage:

This section illustrates intended use of this component.

Example 1: Basic Use of bdlb::CStringLess:

Suppose we need a container to store set of unique C-strings. The following code illustrates how to use bdlb::CStringLess as a comparator for the standard container set, to create a set of unique C-string values.

Note that the default comparator for const char * (i.e., bsl::less<const char *>) compares the supplied addresses, rather than the contents of the C-strings to which those address typically refer. As a result, when using the default comparator, identical C-string values located at different addresses, will be successfully added to a set container. bdlb::CStringLess compares the values of the C-strings ensuring that a set, using CstringLess as a comparator, is a set of unique string values.

First, we create several C-strings:

  const char newYork[]        = "NY";
  const char losAngeles[]     = "LA";
  const char newJersey[]      = "NJ";
  const char sanFrancisco[]   = "SF";
  const char anotherNewYork[] = "NY";

Next, we create two containers, one with default comparator and another using bdlb::CstringLess as a comparator:

  bsl::set<const char *>                    defaultComparatorContainer;
  bsl::set<const char *, bdlb::CStringLess> userComparatorContainer;

Now, we fill containers with the same contents:

  defaultComparatorContainer.insert(newYork);
  defaultComparatorContainer.insert(losAngeles);
  defaultComparatorContainer.insert(newJersey);
  defaultComparatorContainer.insert(sanFrancisco);
  defaultComparatorContainer.insert(anotherNewYork);

  userComparatorContainer.insert(newYork);
  userComparatorContainer.insert(losAngeles);
  userComparatorContainer.insert(newJersey);
  userComparatorContainer.insert(sanFrancisco);
  userComparatorContainer.insert(anotherNewYork);

Finally, we observe that the container created with CStringLess (userComparatorContainer) contains the correct number of unique C-string values (4), while the container using the default comparator does not:

  assert(5 == defaultComparatorContainer.size());
  assert(4 == userComparatorContainer.size());