创建整数2d数组（与字符串2d数组相比）而不提及尺寸

Question

I was trying to create a 2d array without mentioning the dimensions like as follows:

int m1[][] = {{1,2}, {3,4}};

I got the following error when compiled:

error: array type has incomplete element type

Is it not possible to create a 2d array on the stack (as opposed to dynamic memory allocation on heap ) without mentioning the row and column ?

If compiler can't determine the dimension for an integer 2d array, how does it determines the space requirement for string 2d array. For example,

char *keywords[] = {"auto", "static", "extern", "volatile"};

Answer 1

正确，b / c编译器将a）无法确定要分配多少空间，b）无法确定给定元素在数组中的位置。

Answer 2

You can ommit the outer dimension, but not the inner. So this is okay

int m1[][2] = {{1,2}, {3,4}};

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To your second question: char *keywords[] is NOT a 2d array! It is an array of pointers. Pointers are not arrays; Arrays are not pointers! (It's only that arrays decay into pointers to the first element of an array, if used as an rvalue).

Update: To actually answer your question: The strings will typically be statically "allocated" in readonly storage (for example directly written in object files/your program). So it's also wrong to declare your array as char *[] - it should be a const char *[] .