打开双指针字符元素以将其作为文本文件读取时出现问题

Question

我是 C 编程的新手，我正在尝试打开一个 .txt 文件进行阅读。

我有一个文本文件，我想读取不同的文件名，每个文件在不同的行中。我创建了一个函数 txt_to_stations() 读取这个文件并返回一个指向 char 的双指针，我猜它必须是一个双指针，因为我想保存一串 char 字符串。这就是功能。

char** txt_to_stations(const char* txt_file) {

    FILE* file;
    file = fopen(txt_file, "r");
    int line_count = 0;
    int char_count = 0;
    int len = 1;
    char tmp_station[25];
    char** stations = (char**)malloc(len*sizeof(char*));
    char character;
    while(!feof(file)) {
        character = fgetc(file);
        if(character != '\n') {
            tmp_estation[char_count] = character;
            char_count++;
        }else if(character == '\n') {
            stations = (char**)realloc(stations, len*sizeof(char*));
            stations[line_count] = (char*)malloc(char_count*sizeof(char));
            strcpy(stations[line_count], tmp_station);
            len++;
            line_count++;
            char_count = 0;
        }
    }
    fclose(file);
    return stations;
}

我的文本文件是这个。 “站.txt”

weatherdata-429-81.csv
weatherdata-429-84.csv
weatherdata-429-88.csv

当我尝试从 main 函数读取这些文件时，问题就来了。该功能效果很好，因为如果我

char** stations = txt_to_stations("stations.txt")

然后例如

printf("station1: %s\n", stations[0])

它在终端中打印

weatherdata-429-81.csv

.

但是如果我在主函数中定义一个新文件

FILE* reading;
reading = fopen(stations[0]);
if(reading == NULL) {
    printf("csv file cant be opened");
}

它打印“无法打开 csv 文件”，这意味着

fopen(stations[0]) == NULL

，但它不会，因为如果我简单地通过

fopen("weatherdata-429-81.csv")

更改站 [0] 它有效。这可能是一个菜鸟错误，但我明白

stations[0] == weatherdata-429-81.csv (as char*)

我真的尝试过将

stations[0]

(char*) 转换为const char*，并且还在“stations.txt”中将每个名称写入双引号，但无论如何它根本不起作用。我该如何解决这个问题？

Answer 1

我通过调试器运行了你的代码，发现了一些错误。我为您评论了它们（以及其他一些要点）。

char** txt_to_stations(const char* txt_file)
{
    FILE* file;
    file = fopen(txt_file, "r");
    if(file == NULL)  // You forgot to error-check file. fopen is one
                      // of the most likely functions to return NULL,
                      // so you really can't forget that
    {
        printf("Error opening file.");
        exit(0); // Exits your program, regardless of where
                 // you are, defined in stdlib.h
    }

    int line_count = 0;
    int char_count = 0;
    int len = 2;   // I made len slightly bigger, nothing with a
                   // little bit of buffer and also allows you
                   // to keep space for the NULL terminator

    char tmp_station[25] = {0}; // It is always a good idea to zero out
                                // an array you're creating. While testing
                                // I found some stray garbage characters
                                // at the end of one of the strings...

    char** stations = (char**) malloc(len * sizeof(char*));

    char character;

    while (1) // This should run forever and you should break out
              // of this loop when you reach the end of the file
    {
        // This is one way to properly find the end of a file.
        // Don't put feof call inside the while condition
        if (feof(file))
            break;

        // fgets() would save you a lot of time, but oh well,
        // I don't want to change your code too much...
        character = fgetc(file);
        if(character != '\n')
        {
            tmp_station[char_count] = character;
            char_count++;
        }
        else // Removed the if here because it was redundant... else
             // it means that it must be a newline character
        {
            tmp_station[char_count] = '\0';  // You forgot to null-terminate
                                             // the string you took into
                                             // tmp_station. This is the
                                             // main reason the function
                                             // wasn't working
            stations = (char**) realloc(stations, len*sizeof(char*));
            stations[line_count] = (char*) malloc(char_count*sizeof(char));
            strcpy(stations[line_count], tmp_station);
            len++;
            line_count++;
            char_count = 0;

            // It's a good idea to terminate an array of pointers
            // with NULL. How will you know you reached the end
            // of the array?
            stations[line_count] = NULL;
        }
    }
    fclose(file);
    return stations;
}

到目前为止，您的代码存在一个小问题。看，因为你只将一行导入指针数组当且仅当找到换行符，这意味着如果你的

stations.txt

文件的最后一行没有换行符，该行将不会导入到大批。有两种解决方案。

1. 像这样在文本文件末尾添加一个额外的换行符

weatherdata-429-81.csv
weatherdata-429-84.csv
weatherdata-429-88.csv

2. 更改代码，无论是否有换行符，都可以导入最后一行。

3. 使用

   fgets()

   。它将继续读取整个文件，直到到达文件末尾，因此您可以将它返回的任何内容存储在一个数组中，并手动删除它自己生成的换行符。