Cant initialize a 2d array/matrix to 0 [duplicate]

Question

I am trying to initialize a 2d array (matrix) to 0 but, cant do it:

int longestCommonSubsequence(string text1, string text2) {
    int len1=0;
    len1=text1.length()+1;
    int len2=0;
    len2=text2.length()+1;
    int dp[len1][len2]={0};

Error:

Line 8: Char 16: error: variable-sized object may not be initialized
        int dp[len1][len2]={0};
               ^~~~
1 error generated.

I want initialize the matrix while declaring it. I do not want to use for loop.

Variable length array are not standard C++. Moreover, you can't just initialize to zero all the values by just assigning the whole array with zero. I'd suggest you to get a good C++ book and start to learn properly the language. C++ is not a language you can learn just by try and guess. — Fareanor
– Fareanor, Commented Dec 15, 2022 at 12:20
if int dp[len1][len2]; did compile without error, then you are using a compiler extension. If you want to stay with it you need to read your compilers manual. However, its not really recommended, rather aim to write portable code — 463035818_is_not_an_ai
– 463035818_is_not_an_ai, Commented Dec 15, 2022 at 12:23
VLA is not part of C++ standard. This is possible since C has such feature and by default compiler allows to mix C with C++. — Marek R
– Marek R, Commented Dec 15, 2022 at 12:23

Aleksandr Medvedev · Accepted Answer · 2022-12-15 12:32:32Z

2

Variable sized arrays are not standard C++, for arrays of constant length you just use value-initialisation syntax:

int arr[4][4]{};

Alternatively, use C++ collections of variable length:

int rows = 4;
int columns = 4;
std::vector<std::vector<int>> vec(rows, std::vector<int>(columns));

edited Dec 15, 2022 at 12:32

answered Dec 15, 2022 at 12:25

Aleksandr Medvedev

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1 Comment

Aleksandr Medvedev Over a year ago

@rushabhvg you may want to consider C++ standard collections instead. I updated my answer just in case

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