Out of bound access of C++ standard library containers

Index of C++ Standard template Library (STL) container out of bounds during container access using standard operators or methods

Since R2026a

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Description

This defect occurs if an out of bounds element of these containers are accessed using one of the listed operators or methods:

  • std::array — std::array::operator[], std::array::front, std::array::back

  • std::vector — std::vector::operator[], std::vector::push_back, std::vector::pop_back

  • std::deque — std::deque::operator[], std::deque::push_back, std::deque::pop_back, std::deque::push_front, std::deque::pop_front

Risk

Accessing a container outside its bounds is undefined behavior.

Fix

To fix this issue, check the bounds of a container before accessing them. When iterating over containers, avoid using c-style for loops. Instead, use range based for loops that manages the bounds automatically.

Examples

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In this example, the function printArrayElements() prints each element of an std::array container. The upper bound of the for loop is beyond the bounds of the container by one. Polyspace® reports a defect on the [] operator. 

#include <array>
#include <iostream>

void printArrayElements() {
    std::array<int, 5> arr = {1, 2, 3, 4, 5};

    // Off-by-one error
    for (size_t i = 0; i <= arr.size(); ++i) {
        std::cout << arr[i] << std::endl; // Defect
    }
}

Correction — Use correct loop upper bound

To fix this defect, change the upper limit of the loop.

#include <array>
#include <iostream>

void printArrayElements() {
    std::array<int, 5> arr = {1, 2, 3, 4, 5};

    // Off-by-one error fixed
    for (size_t i = 0; i < arr.size(); ++i) {
        std::cout << arr.at(i) << std::endl; // No defect
    }
}
The code also uses the at() operator to access the container elements. If the element is out of bounds, use of at() results in a runtime exception, which makes this bug easier to detect.

Result Information

Group: Programming
Language: C++
Default: On
Command-Line Syntax: CONTAINER_STD_LIB
Impact: High
PQL Name: std.defects.CONTAINER_STD_LIB

Version History

Introduced in R2026a

See Also

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