[英]How to declare global variable by taking value from function
我想將 N 和 M 聲明為全局變量,但我需要從 int main 中獲取 N 和 M 值,那么我該如何實現呢?
#include <stdio.h>
...
int N,M; /*
char board[N][N];
char game_board[N][N]; multiple function using
char (*boardptr)[N]=board;
char (*game_boardptr)[N]=game_board; */
....
int main(int argc,char *argv[])
{
N = atoi(argv[1]);
M = atoi(argv[2]);
....
}
……那么我該如何實現呢?
在C99
及更高版本中,您可以使用VLA來設置數組索引的大小,但 VLA 僅限於local scope ,因此使用此方法,這些在全局范圍內都不合法:
char board[N][N];
char game_board[N][N];
char (*boardptr)[N]=board;
char (*game_boardptr)[N]=game_board;
如果需要全局作用域,還需要動態分配:
int N, M;//indices used to dimension arrays can be global scope
int main(int argc, char *argv[])command line args contain two integer values
{
N = atoi(argv[1]); //use argv[1] & [2]. ( [0] is name of program )
M = atoi(argv[2]);
//if global was not a requirement, you could create arrays like this:
char board[M][N];// VLA - no need to use calloc or malloc
//no need to free memory when finished using the array,
//If global scope is require, this method will work:
char **board = Create2DStr(N, M);
///etc...
return 0;
}
char ** Create2DStr(int numStrings, int maxStrLen)
{
int i;
char **a = {0};
a = calloc(numStrings, sizeof(char *));
for(i=0;i<numStrings; i++)
{
a[i] = calloc(maxStrLen + 1, 1);
}
return a;
}
請注意,此處創建的字符串需要釋放。
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