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C++ Academy · Lesson

Numeric Limits and Overflow Behaviour

Query std::numeric_limits and understand signed and unsigned overflow rules.

Lesson 4 of 413 steps

Numeric Limits and Overflow Behaviour is a free C++ Academy lesson on CoddyKit. This is lesson 4 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the C++ Academy learning path, and your progress syncs across the web and the CoddyKit app. The C++ Academy course includes 4 lessons in total.

Why Limits Matter

Every numeric type has a maximum and minimum representable value. Exceeding them can silently produce wrong results — or undefined behavior.

std::numeric_limits

Query the limits of any numeric type with the <limits> header. Compile-time constants — no runtime cost.

#include <limits>
std::cout << std::numeric_limits<int>::max() << "\n";
std::cout << std::numeric_limits<int>::min() << "\n";
std::cout << std::numeric_limits<double>::epsilon();

Common Queries

The most useful members:

  • max() — largest value
  • min() — smallest (positive) value
  • lowest() — most negative
  • epsilon() — smallest meaningful difference (floats)
  • digits10 — guaranteed decimal digits

Signed Integer Overflow

Signed integer overflow is undefined behavior. The compiler may assume it never happens, leading to surprising optimizations.

int x = std::numeric_limits<int>::max();
x += 1;   // UB — anything can happen

Unsigned Integer Wrap

Unsigned overflow is defined — values wrap around modulo 2^N. This is sometimes useful but often a footgun.

unsigned int u = 0;
u -= 1;   // wraps to 4,294,967,295 (UINT_MAX)

Float Overflow and Underflow

Floats overflow to inf instead of crashing. Underflow goes to subnormal numbers or 0.

double x = 1e308;
x *= 100;
std::cout << x;  // inf

Detecting Overflow Safely

For signed integers, check before the operation. Compilers provide built-in checked-arithmetic helpers like __builtin_add_overflow on GCC/Clang.

if (a > std::numeric_limits<int>::max() - b) {
    // overflow would happen
}
int sum = a + b;

C++20 std::ssize and std::cmp_less

C++20 adds safe integer comparison helpers in <utility>: std::cmp_equal, cmp_less, cmp_greater. They handle signed/unsigned mixing correctly.

Implicit Conversions Are Sneaky

Mixing signed and unsigned in a comparison silently converts the signed operand to unsigned — a common source of subtle bugs.

int a = -1;
unsigned int b = 1;
if (a < b) std::cout << "yes";
else       std::cout << "no";   // prints "no"!

Compile-Time Checks

Use static_assert to enforce size assumptions when writing portable code.

static_assert(sizeof(int) >= 4, "Need at least 32-bit int");

Sanitizers Help in Testing

Build with -fsanitize=undefined to catch signed overflow at runtime during testing.

g++ -fsanitize=undefined -O1 main.cpp

Quick Check

What happens when a signed integer addition overflows in C++?

Answer it in the interactive lesson

Recap

Use std::numeric_limits to query type bounds. Signed overflow is undefined; unsigned wraps. Mix signed and unsigned at your peril. Sanitizers and C++20 safe comparisons help guard your code.

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Frequently Asked Questions

Is the “Numeric Limits and Overflow Behaviour” lesson free?

Yes — any 3 lessons of the C++ Academy learning path, including “Numeric Limits and Overflow Behaviour”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The C++ Academy course includes 4 lessons in total.

What will I learn in “Numeric Limits and Overflow Behaviour”?

Query std::numeric_limits and understand signed and unsigned overflow rules. You practise C++ Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C++ Academy?

No prior experience is required. C++ Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 4 of 4.

How long does the “Numeric Limits and Overflow Behaviour” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this C++ Academy lesson?

Yes. Every C++ Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Integer vs Floating Point Types
  2. The cmath Header: pow sqrt abs round
  3. Random Numbers with the random Header
  4. Numeric Limits and Overflow Behaviour
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