CERT.STR_ACCESS.INVALID

Do not use invalid references, pointers, and iterators to access elements of a basic_string.

The CERT.STR_ACCESS.INVALID checker detects uses of references, pointers, and iterators after an operation invalidates their association with a basic_string. The checker supports intra- and interprocedural cases.

Vulnerability and risk

Operations that modify a basic_string can invalidate references, pointers, and iterators that refer to its elements. Using an invalidated access path results in undefined behavior.

The checker does not report reserve() or shrink_to_fit() calls, because these functions do not always cause reallocation.

Mitigation and prevention

Update an iterator after a mutating operation, or obtain a new pointer or reference only after the operation completes. Avoid using an access path that refers to a string or to its elements after the string has been modified.

Vulnerable code example

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#include <string>

void update(std::string& value)
{
    const char* data = value.data();
    value.replace(0, 2, "bb");
    use(data);
}

The pointer in this example may be invalid after replace() modifies the string. Passing it to use() can result in undefined behavior.

Fixed code example

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#include <string>

void update(std::string& value)
{
    value.replace(0, 2, "bb");
    use(value.data());
}

The fixed example obtains the pointer after the string modification.

External guidance

• CERT STR52-CPP: Use valid references, pointers, and iterators to reference elements of a basic_string