c - 从文件中动态分配二维字符串数组

Question

这个问题可能很常见，但我没有找到任何接近这个确切问题的东西，所以我会问。我有一个看起来像这样的文件。

ABCSTRX
ABCST
ABCS
ABCSTRXY

我的任务是创建二维字符串数组。对于每个字符串，它只分配需要的空间(字符串的长度)，所以它看起来像这样。

到目前为止，在我的代码中，我已经扫描了文件并得到了代表文件中字符串数量的数字。

void function(FILE *txt){
    char arr[50];
    int counter=0;
    char **array;

    do {                                    
       fgets(arr,MAX,txt);
       counter++;
    } while(fgets(arr,MAX,txt)!=NULL);

    rewind(txt);
    array = malloc(counter * sizeof(char*));


    //FROM NOW ON THE CODE IS NOT CORRECT
    do {                                    
        fgets(arr,MAX,txt);
        counter++;

        for(int j=0;j<strlen(arr); j++){
            array[i]= malloc(strlen(arr) * sizeof(char));
            array[i]= arr;
        }
        i++;
    } while(fgets(arr,MAX,txt)!=NULL);

}

问题是我找不到解决方案，如何用大小不匹配的字符串填充动态分配的数组。这是我想出的代码，我觉得卡住了。在数组中填满字符串后，它将被打印出来(我想有两个 for 循环)。感谢评论

Answer 1

您可能需要考虑以下带注释的可编译 C 代码。
我没有在这里写一些注释，而是在代码中插入了一些内联注释，以试图清楚地解释代码的作用。

#include <stdio.h>      /* For printf and file management */
#include <stdlib.h>     /* For dynamic memory allocation */
#include <string.h>     /* For string functions */

/* 
 * Read all lines from text file, and store them in a dynamically 
 * allocated array. 
 * The count of lines is stored in the 'count' output parameter
 * The caller is responsible for freeing the allocated memory.
 */
char** read_lines(FILE* txt, int* count) {
    char** array = NULL;        /* Array of lines */
    int    i;                   /* Loop counter */
    char   line[100];           /* Buffer to read each line */
    int    line_count;          /* Total number of lines */
    int    line_length;         /* Length of a single line */

    /* Clear output parameter. */
    *count = 0;

    /* Get the count of lines in the file */
    line_count = 0;
    while (fgets(line, sizeof(line), txt) != NULL) {                                      
       line_count++;
    }

    /* Move to the beginning of file. */
    rewind(txt);

    /* Allocate an array of pointers to strings 
     * (one item per line). */
    array = malloc(line_count * sizeof(char *));
    if (array == NULL) {
        return NULL; /* Error */
    }

    /* Read each line from file and deep-copy in the array. */
    for (i = 0; i < line_count; i++) {    
        /* Read the current line. */
        fgets(line, sizeof(line), txt);

        /* Remove the ending '\n' from the read line. */
        line_length = strlen(line);        
        line[line_length - 1] = '\0';
        line_length--; /* update line length */

        /* Allocate space to store a copy of the line. +1 for NUL terminator */
        array[i] = malloc(line_length + 1);

        /* Copy the line into the newly allocated space. */
        strcpy(array[i], line);
    }

    /* Write output param */
    *count = line_count;

    /* Return the array of lines */
    return array;
}

int main(int argc, char * argv[]) {
    char**      array    = NULL;    /* Array of read lines */
    FILE*       file     = NULL;    /* File to read lines from */
    const char* filename = NULL;    /* Name of the input file */
    int         i;                  /* Loop index */
    int         line_count;         /* Total number of read lines *7

    /* Get filename from the command line. */
    if (argc != 2) {
        printf("Specify the input file from the command line.\n");
        return 1;
    }    
    filename = argv[1];

    /* Try opening the file. */
    file = fopen(filename, "rt");
    if (file == NULL) {
        printf("Can't open file %s.\n", filename);
        return 1;
    }

    /* Read lines from file. */
    array = read_lines(file, &line_count);

    /* Just for test, print out the read lines. */
    for (i = 0; i < line_count; i++) {
        printf("[%d]: %s\n", (i+1), array[i]);
    }

    /* Cleanup. */
    fclose(file);
    for (i = 0; i < line_count; i++) {
        free(array[i]);
    }
    free(array);
    array = NULL;

    /* All right */
    return 0;
}

使用这样的输入文件:

ABCSTRX
ABCST
ABCS
ABCSTRXY

输出是:

C:\Temp>test.exe testfile.txt
[1]: ABCSTRX
[2]: ABCST
[3]: ABCS
[4]: ABCSTRX