Changing sprintf to an array of characters C++

Question

I have a 2d array of words.

void main() { const int rowsCount = 2; const int colsCount = 5; char*** szData = new char** [rowsCount]; //Allocate memory for each row for (int i = 0; i < rowsCount; i++) { szData[i] = new char* [colsCount]; //how many words in every row for (int j = 0; j < colsCount; j++) { szData[i][j] = new char[15]; //maximum symbols in a word } } //Assign some data for (int i = 0; i < rowsCount; i++) { char s[] = "Williams"; szData[i][0] = s; sprintf(szData[i][0], "Williams%d", 0); sprintf(szData[i][1], "J.%d", 0); sprintf(szData[i][2], "#3%d", 0); sprintf(szData[i][3], "100%d", 0); sprintf(szData[i][4], "01.13%d", 0); } ... }

While assigning data, I tried to change this

sprintf(szData[i][0], "Williams%d");

to this

char s[] = "Williams"; szData[i][0] = s;

Why do I keep getting the message that my project "has trigerred a breakpoint"?

Is there any alternative to sprintf using array of characters? Cannot use string (one of the condition of this task)

Also, not so necessary, but if I delete 0 at the end here

sprintf(szData[i][0], "Williams%d", 0); sprintf(szData[i][1], "J.%d", 0); sprintf(szData[i][2], "#3%d", 0); sprintf(szData[i][3], "100%d", 0); sprintf(szData[i][4], "01.13%d", 0);

there will appear some numbers after every word. For example: Williams3937516. Why is that?

Full code:

#define _CRT_SECURE_NO_WARNINGS #include <iostream> #include <iomanip> #include <conio.h> using namespace std; void main() { const int rowsCount = 2; const int colsCount = 5; char*** szData = new char** [rowsCount]; //Allocate memory for each row for (int i = 0; i < rowsCount; i++) { szData[i] = new char* [colsCount]; //how many words in every row for (int j = 0; j < colsCount; j++) { szData[i][j] = new char[15]; //maximum symbols in a word } } //Assign some data for (int i = 0; i < rowsCount; i++) { char s[] = "Williams"; szData[i][0] = s; sprintf(szData[i][0], "Williams%d"); sprintf(szData[i][1], "J.%d", 0); sprintf(szData[i][2], "#3%d", 0); sprintf(szData[i][3], "100%d", 0); sprintf(szData[i][4], "01.13%d", 0); } //print all the elements for (int i = 0; i < rowsCount; i++) { for (int j = 0; j < colsCount; j++) { cout << szData[i][j] << " "; } cout << endl; } //free memory here for (int i = 0; i < rowsCount; i++) { for (int j = 0; j < colsCount; j++) { delete[] szData[i][j]; } } for (int i = 0; i < rowsCount; i++) { delete[] szData[i]; } delete[] szData; }

If your intent is to write C++ code, you want to use C++ containers, like vectors, to correctly manage all the memory allocations for you, accurately and correctly. The above looks like bug-prone C code instead of C++. Modern C++ rarely needs to use new or delete. There's some kind of a bug in the shown code regarding memory allocation, but rather than wasting time trying to figure out what it is, a much simpler solution is to make it logically impossible for this kind of a bug to happen. Scrap everything, and rewrite it from scratch using modern C++ container and iterator-based code. — Sam Varshavchik
– Sam Varshavchik, Commented Jan 4, 2021 at 16:15
I'm studying at university and cannot do it using vector yet, unfortunately (another condition of the task) — ovvvol
– ovvvol, Commented Jan 4, 2021 at 16:24

Remy Lebeau · Accepted Answer · 2021-01-04 19:05:59Z

If you trace back the assignment of this pointer:

char s[] = "Williams";

You'll find you are attempting to free its memory here:

delete[] szData[i][j];

However, you can't do that -- the string "Williams" was never allocated with new, so it can't be freed with delete. In fact, it's statically allocated, in your binary. So the heap complains, and that's the cause of the breakpoint.

If you're going to delete everything in szData, you need to make sure it's all allocated on the heap with new.

Second problem - when you call:

sprintf(szData[i][0], "Williams%d", 0);

You're overwriting the bounds of the memory you supplied. Remember, your buffer only has "Williams" number of bytes (plus one)! You don't have space to tack an integer's string representation on the end of that. Use sprintf_s and make sure your buffers have enough room!

Third problem - writing to statically allocated string data is enormously sketchy and may not work in all cases.

Bottom line: dynamic allocate a buffer of the right size for everything, and your code will work.

Here's a simple example to fix that section of code. It demonstrates the concepts that fix your code, but it's not really appropriate for your codebase as-is, you'll need to work it in properly.

const size_t MAX_NAME_LENGTH = 15; // Fix this magic number to be whatever max name length you want char *s = new char[MAX_NAME_LENGTH]; // allocate on heap strcpy_s(s, MAX_NAME_LENGTH, "Williams"); // use strcpy_s for safety szData[i][0] = s; sprintf_s(szData[i][0], MAX_NAME_LENGTH, "Williams%d", 0); // use sprintf_s for safety

strcpy_s and sprintf_s are optional in Standard C++ (many compilers may not provide them)

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