在C99模式之外使用'for'循环初始声明

Question

Any ideas why I am getting that error? I thought I'd done everything fine, it wasn't showing any errors before I coded past it?

for (int i=0;i<height;i++)
{
    if (i == 0 || i == height-1 )
    {
        for (int j=0;j<width;j++)
        {
            printf("%i_",paddings);
            if (j == width-1)
            {
                printf("%i\n",paddings);
            }
        }
    }

Answer 1

This is a hold-back from the days of ANSI C. Basically, it means that you must declare variables for use in for loops like so:

// Looping variables declared outside the loops
int i, j;

for (i = 0; i < n; i++)
{
    if (i == 0 || i == height - 1)
    {
        for (j = 0; j < width; j++)
        {
            printf("%i_", paddings);
            if (j == width - 1)
            {
                printf("%i\n", paddings);
            }
        }
    }
}

Alternatively, you could change your compiler flags so that it uses C99 or above. For gcc this would simply entail adding the compile flag -std=c99 , or for C11, -std=c11

Answer 2

for (int i = 0; ...)

is a C99 extension; in order to use it you must enable it via specific compiler flags in gcc

For old standards like C89 is:

int i;
for (i = 0; ...)

You must declare your variables outside the loop.