从命令行定义全局数组的大小

发布于 2024-10-04 20:22:12 字数 800 浏览 7 评论 0原文

我正在做一项作业，需要使用 pthread 或信号量来同步某些访问某些共享资源的进程。由于我们课堂上的所有示例都使用全局变量作为共享资源，因此我计划做同样的事情，但我想将共享资源的值基于命令行参数。 我知道如何在主方法中使用命令行参数，但如何根据命令行参数定义全局数组（共享资源）的大小？

更新：

沃利克的答案似乎会起作用，但我对一些更精细的细节仍然模糊。请参阅示例和评论...

#include <stdio.h>

void print_array(void);

int *array;
int count;

int main(int argc, char **argv){
    int count = atoi(argv[1]);
    array = malloc(count *sizeof(array[0]));
    int i;
    for(i = 0; i < count; i++){ /*is there anyway I can get the size of my array without using an additional variable like count?*/
        array[i] = i;
    }
    print_array();
    return 0;
}

void print_array(){
    int i;
    for(i = 0; i < count; i++){
        printf("current count is %d\n", array[i]);
    }
}

原文

I am doing an assignment where I need to use pthreads or semaphores to synchronize some processes which access some shared resource. Since all of our examples in class use a global variable as the shared resource I planned on doing the same thing, but I wanted to base the value of the shared resource on a command line argument. I know how to use command line arguments within my main method, but how do I define the size of a global array (the shared resource) based on a command line argument?

Update:

Wallyk's answer seems like it will work, but I'm still fuzzy on some of the finer details. See the example and comments...

#include <stdio.h>

void print_array(void);

int *array;
int count;

int main(int argc, char **argv){
    int count = atoi(argv[1]);
    array = malloc(count *sizeof(array[0]));
    int i;
    for(i = 0; i < count; i++){ /*is there anyway I can get the size of my array without using an additional variable like count?*/
        array[i] = i;
    }
    print_array();
    return 0;
}

void print_array(){
    int i;
    for(i = 0; i < count; i++){
        printf("current count is %d\n", array[i]);
    }
}

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灯角 2024-10-11 20:22:12

您不能执行静态动态声明，例如：

int globalarray[n];

其中n是在运行时设置的变量。这是行不通的，因为数组是在程序开始运行之前初始化的。

一个好的替代方法是使用指向动态内存的指针：

int *globalarray;

int main (int argc, char **argv)
{
...
   int elements = atoi (argv [j]);  // parse out the program argument array size
   globalarray = malloc (elements * sizeof (globalarray[0]));
}

You can't do a static dynamic declaration like:

int globalarray[n];

Where n is a variable set at runtime. This doesn't work because the array is initialized before the program begins running.

A good alternative is to use a pointer to dynamic memory:

int *globalarray;

int main (int argc, char **argv)
{
...
   int elements = atoi (argv [j]);  // parse out the program argument array size
   globalarray = malloc (elements * sizeof (globalarray[0]));
}

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