时间戳

首页 > 解决方案 > 动态数组分配仅返回所有索引中的最后一个元素 C

c - 动态数组分配仅返回所有索引中的最后一个元素 C

问题描述

好的，所以我正在尝试将文本文件中的数据输入到字符串的动态数组中。每个数据元组有 6 个属性。因此有 6 个数组。问题是当我填充所有数组时，它会在循环中打印正确的值。但是当我尝试访问循环外的任何数组元素时，它会给出文本文件的最后一个单词作为输出。我已经尝试了所有可用的解决方案，但它们似乎都不起作用。

代码是：

int  n(FILE **fp, int size,  char **presenters, char **birth_numbers, char **room_codes, 
        char **authors, char **post_titles, char **presentation_types, char **presentation_times, 
        char **dates){
    // Buffer to get input from the file.
    char buffer[200];
    // To check if the file is open or not
    if (*fp == NULL){
        printf("File not Open");
    }
    else{
        char *file = "konferencny_zoznam.txt";
        fseek(*fp, 0, SEEK_SET);
        if (size >= 1){
            int length_of_arrays = sizeof presenters / sizeof *presenters;
            if (length_of_arrays > 1){
                printf("in null if");
                free(presenters);
                free(birth_numbers);
                free(room_codes);
                free(authors);
                free(post_titles);
                free(presentation_times);
                free(presentation_types);
                free(dates);
            }

            presenters = malloc((size+1)* sizeof(char*));
            birth_numbers = malloc((size+1)* sizeof(char*));
            room_codes = malloc((size+1)* sizeof(char*));
            authors = malloc((size+1)* sizeof(char*));
            post_titles = malloc((size+1)* sizeof(char*));
            presentation_times = malloc((size+1)* sizeof(char*));
            presentation_types = malloc((size+1)* sizeof(char*));
            dates = malloc((size+1)* sizeof(char*));

            const unsigned MAX_BUFFER_LENGTH = 256;
            char buffer[MAX_BUFFER_LENGTH];
            int i = 0, len = 0;
        

            while(fgets(buffer, MAX_BUFFER_LENGTH, *fp)){
                // len = strlen(buffer)+1;
                presenters[i] = buffer;
                fgets(buffer, MAX_BUFFER_LENGTH, *fp);
                birth_numbers[i] = buffer;
                fgets(buffer, MAX_BUFFER_LENGTH, *fp);
                room_codes[i] = buffer;
                fgets(buffer, MAX_BUFFER_LENGTH, *fp);
                authors[i] = buffer;
                fgets(buffer, MAX_BUFFER_LENGTH, *fp);
                post_titles[i] = buffer;
                fgets(buffer, MAX_BUFFER_LENGTH, *fp);
                presentation_times[i] = buffer;
                fgets(buffer, MAX_BUFFER_LENGTH, *fp);
                presentation_types[i] = buffer;
                fgets(buffer, MAX_BUFFER_LENGTH, *fp);
                dates[i] = buffer;
                printf("buffer : %s", dates[i]);
                fgets(buffer, MAX_BUFFER_LENGTH, *fp);

                i++;
            }
       
            for (int i=0; i<8; i++){
                
                printf("presenter[0]: %s", dates[i]);
                // Outputs 20200406 for each iteration which is the last word of file.

            }
        }
        else {
            printf("File not read already. Consider running command v before.");
        }
    }
}

标签： cmallocdynamic-memory-allocationdynamic-arrayspass-by-value

解决方案

你不能做

array[i] = buffer;

因为缓冲区是一个 char 数组，并存储了 char 数组的地址。当您将其值分配给一个新变量时，您基本上是将其地址复制到一个新变量中。这就是为什么您的数组的每个索引都指向同一个数组，该数组包含文件中的最新值。

您需要通过 strcpy 或其他方式复制缓冲区变量的内容来执行深层复制。

推荐阅读