Vector going out of bounds without giving error

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I have a std::vector. I check its size which is 6 but when I try to access vec[6] to check whether it will give error, I get no error but some number instead. Should not it give an error?

edit: something like:

struct Element
{
    std::vector<double> face;
};

int main()
{
    Element elm;

    .... // insert 6 elements into elm.face

    std::cout << elm.face.size() << std::endl; // answer is 6
    std::cout << elm.face[6] << std::endl; // answer is some number
}

STL vectors perform bounds checking when the .at() member function is called, but do not perform any checks on the [] operator.

When out of bounds, the [] operator produces undefined results.

Quick Q: Vector going out of bounds without giving error : Standard , Quick Q: Vector going out of bounds without giving error STL vectors perform bounds checking when the .at() member function is called, but� I want to confirm that if i make that particular method synchronized, is it going to solve my problem. No it wont, but it helps if you make it synchronized, and always checks the size before you try to access the element.

Vector going out of bounds without giving error, I have a std::vector. I check its size which is 6 but when I try to access vec[6] to check whether it will give error, I get no error but some number� when "repeat x-times" option is setted, exception occures. Dismiss Join GitHub today. GitHub is home to over 50 million developers working together to host and review code, manage projects, and build software together.

It's undefined behavior. Undefined behavior does not necessarily mean you'll get an error: you might, but you might instead get some result that doesn't make much sense.

4. Index Out of Bounds - Safe C++ [Book], Index Out of Bounds There are several ways in C++ to create an array of In addition to allowing you to catch this index-out-of-bounds error, the template vector has If you cross-use these operators ( new with brackets and delete without or� struct LandDetails { // declaring a class public: string Surname, OtherNames, LandNum, KraPin, OwnerIdCard, address, LandCounty, LandDist, LandDiv, Landloc, LandSubloc; //function will read a file into a vector, a line is searched that //correspond user input, the record found is modified by a string, //the file so modified is passed to another

Data structures are indexed starting at 0, so if you are accessing vec[6] then this is going to be out of bounds. You are likely not getting an error due to a memory issue; there could be something there from previous code you have run, or some similar error. Please post code.

vector::at - C++ Reference, Strong guarantee: if an exception is thrown, there are no changes in the container. It throws out_of_range if n is out of bounds. See also. vector::operator[]: Access� Stay inside the bounds of the array in C programming while using arrays to avoid any such errors. C++ however offers the std::vector class template, which does not require to perform bounds checking.

Vector going out of bounds without givin - C++ Forum, When i run this program, i create a vector succesfully, but in the next loop the program stops working without giving an error. when i trie to cout� While very atypical, you can also use the .at() member function to "safely" access a vector's elements at runtime. The at() member is just like operator[] but it will check the bounds automatically and throw a C++ exception if the index is illegal, which can be caught and handled by your code. This usage is uncommon, especially in games, due to the performance overhead of checking bounds along with the unpopularity of C++ exceptions in the game industry.

ATTENTION, we are about to test index-out-of-bounds for STL vector reference to scpp::vector Value of vector at 0 is 0 Value of vector at 1 is 1 Value of vector at 2 is 2 Value of vector at 3 is 1 Note that the code happily prints the value at the index 3, even though the maximum valid index is 2, which means that our sanity check did not work

Generally, an array is of fixed size and each element is accessed using the indices. For example, we have created an array with size 9. Then the valid expressions to access the elements of this array will be a[0] to a[8] (length-1).

Comments
  • size 6, so last is vec[5] starts with 0
  • Not sure where you got the idea that vector would throw an error on an invalid index using operator[]. The docs certainly say otherwise.
  • Notice that the first element has a position of 0 (not 1). -- cplusplus.com/reference/vector/vector/operator[]
  • @Koushik: Because it slows things down. That's what at() is for
  • 11 upvotes for simply failing to consult the documentation. Why?
  • The behavior is undefined, so implementations are allowed to introduce bounds checks; the difference from at is that bounds checks are required for at.
  • ...may run significantly slower in debug mode on a microsoft system.