将文件中的文本逐行插入到指针传递的字符串数组中的函数 [英] Function to insert text line by line from a file into string array passed by pointer

问题描述

我正在尝试创建一个函数read_lines，该函数需要一个文件* fp，一个指向char **行的指针以及一个指向int num_lines的指针.该函数应将每一行文本插入到行中，并将num_lines增加到文件包含的行数.

I'm trying to create a function read_lines that takes a file *fp, a pointer to char** lines, and pointer to int num_lines. The function should insert each line of text into lines, and increase num_lines to however many lines the file has.

这可能真的很简单，但是我已经尝试插入文本几个小时了.

Its probably really simple but I've been trying to insert the text for several hours now.

这是main.c的外观.除了read_lines之外的所有东西都已经定义并且可以正常工作.

This is what main.c would look like. Everything but read_lines is already defined and working.

int main(int argc, char* argv[]){

    char** lines = NULL;
    int num_lines = 0;
    FILE* fp = validate_input(argc, argv);
    read_lines(fp, &lines, &num_lines);
    print_lines(lines, num_lines);
    free_lines(lines, num_lines);
    fclose(fp);

    return 0;
}

这是我尝试添加行的尝试之一，但我无法弄清楚.

This is one of my attempts at trying to append lines, but I couldn't figure it out.

read_lines.c

read_lines.c

void read_lines(FILE *fp, char ***lines, int *num_lines) {
    int i;
    int N = 0;
    char s[200];
    for (i=0; i<3; i++)
    {
        while(fgets(s, 200, fp)!=NULL){N++;}
        char strings[50][200];

        rewind(fp);
        fgets(s, 200, fp);
        strcpy(lines[i],s);
    }

}

感谢您为解决此问题提供的帮助.

I'd appreciate any help at solving this, thanks.

推荐答案

一种解决方案(不包含标头和用于可读性的错误检查):

A solution (without headers and error checking for readability):

void read_lines(FILE *stream, char ***lines_ptr, size_t *num_lines_ptr) {
   char **lines = NULL;
   size_t num_lines = 0;
   char *line = NULL;
   size_t len = 0;
   ssize_t nread;
   while ((nread = getline(&line, &len, stream)) != -1) {
      lines = lines == NULL
         ? malloc(sizeof(char*))
         : realloc(lines, (num_lines+1)*sizeof(char*));

      lines[num_lines] = malloc(nread+1);
      memcpy(lines[num_lines], line);
      ++num_lines;
   }

   free(line);
   *lines_ptr = lines;
   *num_lines_ptr = num_lines;
}

完整解决方案:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// lines_ptr:     Output. Initial value ignored. To be freed by caller on success.
// num_lines_ptr: Output. Initial value ignored.
// Returns:       0 on error (errno set). 1 on success.
int read_lines(FILE *stream, char ***lines_ptr, size_t *num_lines_ptr) {
   char ***lines = NULL;
   size_t num_lines = 0;
   char *line = NULL;
   size_t len = 0;
   ssize_t nread;
   while ((nread = getline(&line, &len, stream)) != -1) {
      char **new_lines = lines == NULL
         ? malloc(sizeof(char*))
         : realloc(lines, (num_lines+1)*sizeof(char*));
      if (new_lines == NULL)
         goto error;

      lines = new_lines;

      lines[num_lines] = malloc(nread+1);
      if (lines[num_lines] == NULL)
         goto error;

      memcpy(lines[num_lines], line);
      ++num_lines;
   }

   if (ferror(stream))
      goto error;

   free(line);
   *lines_ptr = lines;
   *num_lines_ptr = num_lines;
   return 1;

error:
   for (size_t i=num_lines; i--; )
      free(lines[i]);

   free(lines);
   free(line);
   *lines_ptr = NULL;
   *num_lines_ptr = 0;
   return 0;
}

(您可以使用..._ptr变量来保存三行，而不必在末尾设置它们，但这真的值得您付出可读性吗?)

(You could save three lines by using the ..._ptr vars instead of setting them at the end, but is that really worth the readability cost?)

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