[英]variable-sized object may not be initialized
So this section of code generates a huge amount of errors but it works when I have InputM[3][3] = blah 因此,这部分代码会产生大量错误,但是当我有InputM [3] [3] = blah时它会起作用
Why would this be. 为什么会这样。 For reference, code:
供参考,代码:
int n = 3;
printf("%ld\n", n);
double InputM[n][n] = { { 2, 0, 1 }, { 3, 1, 2 }, { 5, 2, 5} };
Generates: 产生:
prog3.c: In function 'main':
prog3.c:47: error: variable-sized object may not be initialized
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM[0]')
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM[0]')
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM[0]')
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM')
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM[0]')
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM[0]')
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM[0]')
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM')
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM[0]')
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM[0]')
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM[0]')
prog3.c:47: warning: excess elements in array initializer
prog3.c:47: warning: (near initialization for 'InputM')
Compile-time, you compiler does not know how many elements are in your matrix. 编译时,编译器不知道矩阵中有多少元素。 In C, you can dynamically allocate memory using malloc.
在C中,您可以使用malloc动态分配内存。
You could use a define to create a constant value: 您可以使用define来创建常量值:
#define N 3
int main()
{
double InputM[N][N] = { { 2, 0, 1 }, { 3, 1, 2 }, { 5, 2, 5} };
}
Or malloc: 或者malloc:
int main()
{
int n = 3;
int idx;
int row;
int col;
double **inputM;
inputM = malloc(n * sizeof(double *));
for (idx = 0; idx != n; ++idx)
{
inputM[idx] = malloc(n * sizeof(double));
}
// initialise all entries on 0
for (row = 0; row != n; ++row)
{
for (row = 0; row != n; ++row)
{
inputM[row][col] = 0;
}
}
// add some entries
inputM[0][0] = 2;
inputM[1][1] = 1;
inputM[2][0] = 5;
}
In C99, variable-sized array can't be initialized, why ? 在C99中,可变大小的数组无法初始化,为什么?
Because at the compile time, the compiler doesn't know the exact size of array, so you cannot initialize it. 因为在编译时,编译器不知道数组的确切大小,所以您无法初始化它。
n will be evaluated at runtime, then your array will be allocated on the stack-frame. n将在运行时进行评估,然后您的数组将在堆栈帧上分配。
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