Home GetConsoleScreenBufferInfo returning wierd values when called using function

Questions

GetConsoleScreenBufferInfo returning wierd values when called using function

May 27, 2024

I have a program where I want to print out the size of the terminal window in columns and rows.

To do this I want to call this function from int main():

int getConsoleSize(){
    CONSOLE_SCREEN_BUFFER_INFO csbi;
    int columns, rows;

    GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &csbi);
    columns = csbi.srWindow.Right - csbi.srWindow.Left + 1;
    rows = csbi.srWindow.Bottom - csbi.srWindow.Top + 1;

    return columns, rows;
}

int main() looks like this:

int main(){
    int columns, rows = getConsoleSize();
    printf("columns: %d\n", columns);
    printf("rows: %d\n", rows);

    //prevent window from closing
    getc(stdin);

    return 0;
}

When calling the function getConsoleSize() it gives me the output columns: 5990652\n rows: 30 which is clearly not correct. The columns output is also not consistent but is always at least 6-7 numbers long.
But when the code is copy pasted from the function directly into main() it seems to return the correct values with the outputs columns: 120\n rows: 30.

Why is this and how do I fix it so that the function return the correct values.

>Solution :

You cannot return 2 values like that from the function getConsoleSize.

The function is returning only 1 int – the rows in this case.
columns is main remains uninitialized and what you see is a "garbaged" value.

In order to get both dimensions you can change getConsoleSize to get 2 parameters as int* (pointer to int), and dereference the pointers to update the dimensions in main.

You should also check the return value from GetConsoleScreenBufferInfo to verify it succeeded.

The success/failure status should also be returned from getConsoleSize as a boolean and checked in main.

#include <Windows.h>
#include <stdio.h>


BOOL getConsoleSize(int * cols, int * rows) 
{
    CONSOLE_SCREEN_BUFFER_INFO csbi;
    if (!GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &csbi))
    {
        return FALSE;
    }
    // TODO: make sure cols, rows are not NULL
    *cols = csbi.srWindow.Right - csbi.srWindow.Left + 1;
    *rows = csbi.srWindow.Bottom - csbi.srWindow.Top + 1;
    return TRUE;
}


int main() 
{
    int columns, rows;
    if (!getConsoleSize(&columns, &rows))
    {
        printf("FAILED\n");
        return EXIT_FAILURE;
    }
    printf("columns: %d\n", columns);
    printf("rows: %d\n", rows);
    getc(stdin);
    return EXIT_SUCCESS;
}

Possible output: