如何在 C 语言中为文件行分配内存

Question

我创建了应该查找文件中行数的函数(find_numlines(((和一个将文件行读取到char***行(read_lines(((中的函数。 提供了我的主要函数中的其余功能，因此问题不在这些功能中。

read_lines.c(更新(：

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

int findnum_lines(FILE* fp){
  int num_lines = 0;
  int line;
  line = getc(fp);
  if (line != EOF) {
    num_lines++;
    do {
      if (line == 'n') {
        num_lines = num_lines + 1;
      }
      line = getc(fp);
    }
    while (line != EOF);
  }
  rewind(fp);
  return num_lines;
}

void read_lines(FILE* fp, char*** lines, int* num_lines){
  int i;
  (*lines) = malloc(*num_lines * sizeof(char*));
  for (i=0; i < *num_lines; i++)
  {
    (*lines)[i] = malloc(1000);
    (*lines)[i][0] = '';
    fgets((*lines)[i], 1000, fp);
  }
}

主.c ：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include "read_lines.h"

void print_lines(char** lines, int num_lines){
    int i;
    for(i = 0 ; i < num_lines; ++i){
        printf("%d. %s", i+1, lines[i]);
    }
}
void free_lines(char** lines, int num_lines){
    int i;
    for(i = 0 ; i < num_lines; ++i){
        free(lines[i]);
    }
    if(lines != NULL && num_lines > 0){
        free(lines);
    }
}
FILE* validate_input(int argc, char* argv[]){
    FILE* fp = NULL;
    if(argc < 2){
        printf("Not enough arguments entered.nEnding program.n");
        exit(0);
    }
    else if(argc > 2){
        printf("Too many arguments entered.nEnding program.n");
        exit(0);
    }
    fp = fopen(argv[1], "r");
    if(fp == NULL){
        perror("fopen");
        printf("Unable to open file: %snEnding program.n", argv[1]);
        //fprintf(stderr, "Unable to open file %s: %sn", argv[1], strerror(errno));
        exit(0);
    }
    return fp;
}

int main(int argc, char* argv[]){
    char** lines = NULL;
    int num_lines = 0;
    FILE* fp = validate_input(argc, argv);
    num_lines = findnum_lines(fp);
    read_lines(fp, &lines, &num_lines);
    print_lines(lines, num_lines);
    free_lines(lines, num_lines);
    fclose(fp);
    return 0;
}

read_lines.h ：

#ifndef READ_LINES
    #define READ_LINES
    #include <stdio.h>
    void read_lines(FILE* fp, char*** lines, int* num_lines);
    int findnum_lines(FILE* fp);
#endif

每当我输入文件时，find_numlines()都会返回正确的行数，但read_lines()出现问题lines因为仍然NULL。

示例文件normal.txt：

Hello Class
This is what I would call a normal file
It isn't very special
But it still is important

尾声应为：

1. Hello Class
2. This is what I would call a normal file
3. It isn't very special
4. But it still is important

Answer 1

在下面的代码中，我添加了 rewind 命令(由 xing 提及(以及每行和"行表"的内存分配。对用于计算行数和错误处理的代码进行了进一步的改进。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int findnum_lines(FILE* fp){
  int num_lines = 0;
  int c;
  c = getc(fp);
  if (c != EOF) {
    num_lines++;
    do {
        if (c == 'n') {
            num_lines = num_lines + 1;
        }
        c = getc(fp);
    }
    while (c != EOF);
  }
  rewind(fp);
  return num_lines;
}
void read_lines(FILE* fp, char*** lines, int* num_lines){
  int i;
  // allocate memory for pointers to start of lines
  (*lines) = malloc(*num_lines * sizeof(char*));
  for (i=0; i < *num_lines; i++)
  {
    (*lines)[i] = malloc(1000);
    (*lines)[i][0] = ''; // terminate for the case that last line does not contain characters
    fgets((*lines)[i], 1000, fp); // read up to 999 characters and terminate string
  }
}
void print_lines(char** lines, int num_lines){
    int i;
    for(i = 0 ; i < num_lines; ++i){
        printf("%d. %s", i+1, lines[i]);
    }
    printf("n");
}
void free_lines(char** lines, int num_lines){
    int i;
    for (i = 0 ; i < num_lines; ++i) {
        if (lines[i]!=NULL) {
            free(lines[i]);
        }
    }
    if (lines != NULL){
        free(lines);
    }
}
FILE* validate_input(int argc, char* argv[]){
    FILE* fp = NULL;
    if (argc < 2){
        printf("Not enough arguments entered.n");
    }
    else if (argc > 2){
        printf("Too many arguments entered.n");
    }
    else {
        fp = fopen(argv[1], "r");
        if (fp == NULL){
            printf("Unable to open file: %sn", argv[1]);
        }
    }
    return fp;
}

int main(int argc, char* argv[]){
    char** lines = NULL;
    int num_lines = 0;
    FILE* fp = validate_input(argc, argv);
    if (fp != NULL)
    {
        num_lines = findnum_lines(fp);
        read_lines(fp, &lines, &num_lines);
        print_lines(lines, num_lines);
        free_lines(lines, num_lines);
        fclose(fp);
    }
    return 0;
}