Question

关于如何在C中连接char数组有很多问题，但是我想知道的与此不同。我想知道如何在C中连接“双指针” char数组。

例如，

const char *array1[] = {"aa", "bb"};
const char *array2[] = {"cc", "dd", "ee"};

我想像这样获得新的char双指针数组：

char **new_array = {"aa", "bb", "cc", "dd", "ee"};
// this code actually doesn't work, though

我想知道最简单，最快的方法。

编辑：实际上，我打算在下面创建一个程序。

int main(int argc, char **argv) {
    pid_t pid;
    char **args = {"sh", "-c"} + argv; // this code doesn't work
    posix_spawn(&pid, "/bin/sh", NULL, NULL, (char* const*)args, NULL);
}

该程序只在“ sh -c”之后传递参数。

Answer 1

当然，只需为此分配一个缓冲区

#define _GNU_SOURCE 1
#include <stdio.h>
#include <strings.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
int main()
{
    #define ARRAY_SIZE(x)  (sizeof(x) / sizeof(x[0]))
    const char * const array1[] = {"aa", "bb"};
    const size_t array1_size = ARRAY_SIZE(array1);
    const char * const array2[] = {"cc", "dd", "ee"};
    const size_t array2_size = ARRAY_SIZE(array2);
    const size_t concat_len = array1_size + array2_size;
    const char ** const concat = malloc(concat_len * sizeof(*concat));

    assert(concat != NULL);
    for (size_t i = 0; i < concat_len; ++i) {
        concat[i] = strdup(i < array1_size ? array1[i] : array2[i - array1_size]);
        assert(concat[i] != NULL);
    }

    for (size_t i = 0; i < concat_len; ++i) {
        printf("concat[%zu] = (%zu) '%s'\n", i, strlen(concat[i]), concat[i]);
    }

    for (size_t i = 0; i < concat_len; ++i) {
        free(concat[i]);
    }
    free(concat);

    return 0;
}

但是我们应该能够做得更好。

Answer 2

class ImageUI {

    private Context context;
    private ArrayList<String> urls = new ArrayList<>();

    private ImageView imageView;
    private ProgressBar progressBar;
    private LinearLayout linearLayoutScrollView;

    public ImageUI(Context context, ArrayList<String> urls, LinearLayout linearLayoutScrollView) {
        this.context = context;
        this.urls = urls;
        this.linearLayoutScrollView = linearLayoutScrollView;
    }

    private void buildUI() {
        System.out.println("Error # 1");
        imageView = new ImageView(context);
        imageView.setVisibility(View.GONE);

        System.out.println("Error # 2");
        progressBar = new ProgressBar(context);
        progressBar.setIndeterminate(true);
        progressBar.setVisibility(View.GONE);

        System.out.println("Error # 3");
        RelativeLayout relativeLayout = new RelativeLayout(context);
        relativeLayout.setGravity(1);
        relativeLayout.addView(imageView);
        relativeLayout.addView(progressBar);
//
//        System.out.println("Error # 4");
//        linearLayoutScrollView = (LinearLayout) linearLayoutScrollView.findViewById(R.id.linearLayoutScrollView);
        linearLayoutScrollView.addView(relativeLayout);
//        System.out.println("Error # 5");

    }

    void downloadImages() {
        int i = 0;
        while (i < urls.size()) {

            buildUI();

            ImageDownloader imageDownloader = new ImageDownloader(imageView, progressBar/*,imageDownloader*/);

            progressBar.setVisibility(View.VISIBLE);

            imageDownloader.execute(urls.get(i));


            imageDownloader = null;

            i++;
        }
    }

}

在C中串联双指针char数组

2 个答案: