Prefer the standard library to other libraries and to "handcrafted code"

Reason

Code using a library can be much easier to write than code working directly with language features, much shorter, tend to be of a higher level of abstraction, and the library code is presumably already tested. The ISO C++ Standard Library is among the most widely known and best tested libraries. It is available as part of all C++ implementations.

Example

auto sum = accumulate(begin(a), end(a), 0.0);   // good

a range version of accumulate would be even better:

auto sum = accumulate(v, 0.0); // better

but don't hand-code a well-known algorithm:

int max = v.size();   // bad: verbose, purpose unstated
double sum = 0.0;
for (int i = 0; i < max; ++i)
    sum = sum + v[i];

Exception

Large parts of the standard library rely on dynamic allocation (free store). These parts, notably the containers but not the algorithms, are unsuitable for some hard-real-time and embedded applications. In such cases, consider providing/using similar facilities, e.g., a standard-library-style container implemented using a pool allocator.

Enforcement

Not easy. ??? Look for messy loops, nested loops, long functions, absence of function calls, lack of use of built-in types. Cyclomatic complexity?