c - 如何修复打印使用双字符指针在文件中读取的代码的代码

Question

这段代码的目的是读取两个文件的内容，并将它们存储到两个双字符指针中，以便每个数组的每个元素存储每个文件的一行。读取文件时，我告诉程序打印这些行，它会完全按照写入的方式打印。但是，当我尝试在 foo 循环之外打印数组甚至整个数组本身的随机元素时，程序返回 NULL 或不打印任何内容。

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


int main() {

    //Opening the files
    FILE * file_1 = fopen("file1.ll", "r");
    FILE * file_2 = fopen("file2.ll", "r");
    if (file_1 == NULL || file_2 == NULL) {
        perror("Error opening file\n");
    }
    //Here I create a temporary string
    char temp_string [1000];
    // I create an array of strings
    char ** string_1 = (char **)malloc (sizeof(char * ) * 1000);
    int i = 0;
    //size_1 and size_2 will be used to account for the effective size of the arrays
    int size_1 = 0, size_2 = 0;
    //I read the file into temp_string
    while (fgets(temp_string, 1000, file_1) != NULL) {
        string_1[i] = (char *) malloc (sizeof(char) * 1000);
        //Then I copy temp_string to the element i of string_1
        strcpy (string_1[i], temp_string);
        //I print the string
        fputs(string_1[i], stdout);
        //and increase the size
        size_1++;
    }

    printf("\n\n\n\n\n\n\n\n\n\n\n");
    //I do the same for file 2
    char temp_string_2 [1000];
    char ** string_2 = (char **)malloc (sizeof(char * ) * 1000);
    while (fgets(temp_string_2, 1000, file_2) != NULL) {
        string_2[i] = (char *) malloc (sizeof(char) * 1000);
        strcpy (string_2[i], temp_string_2);
        fputs(string_2[i], stdout);
        size_2++;
    }
    //Until now everything is okay. The compiler warns nothing and the code is read and printed.
    //I've put big spaces to facilitate the reading of the code
    printf("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");

    //Here I try to print the first four elements of string_1, but string_1[2] and
    //string_1[3] return NULL
    printf("%s%s%s%s\n\n", string_1[0], string_1[1],string_1[2],string_1[3]);

    printf("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");

    //Here only two lines are printed
    for (int i=0; i<size_1; i++) {
        fputs(string_1[i], stdout);
    }
    printf("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");
    for (int i=0; i<size_2; i++) {
        fputs(string_2[i], stdout);
    }

    system("pause");
    return 0;
}

Answer 1

以下建议代码:

1. 更正 OP 问题评论中指出的问题
2. 正确检查 I/O 和堆分配错误
3. 正确检查每个缓冲区不会被大文件溢出
4. 避免分配不需要的本地缓冲区
5. 干净地编译
6. 执行所需的功能
7. 自行清理
8. 定义有意义的名称以避免使用“神奇”数字

现在，建议的代码:

#include <stdio.h>   // fopen(), perror(), FILE
#include <stdlib.h>  // exit(), EXIT_FAILURE, malloc(),  calloc()
#include <string.h>  // strcpy()

#define  MAX_LINES     1024
#define  MAX_LINE_LEN  1024


void cleanup( FILE* file1, FILE* file2, char **array1, char **array2 )
{
    if( file1 )
        fclose( file1 );

    if( file2 )
        fclose( file2 );

    if( array1 )
    {
        for( size_t i = 0; array1[i]; i++ )
            free( array1[i] );
        free( array1 );
    }

    if( array2 )
    {
        for( size_t i = 0; array2[i]; i++ )
            free( array2[i] );
        free( array2 );
    }
}


int main( void ) 
{
    FILE *file_1 = NULL;
    FILE *file_2 = NULL;
    char ** string_1 = NULL;
    char ** string_2 = NULL;

    //Opening the files
    if( !( file_1 = fopen("file1.ll", "r") ) )
    {
        perror( "fopen for file1.ll failed" );
        cleanup( file_1, file_2, string_1, string_2 );
        exit( EXIT_FAILURE );
    }

    if( !( file_2 = fopen("file2.ll", "r") ) )
    {
        perror( "fopen for file2.ll failed" );
        cleanup( file_1, file_2, string_1, string_2 );
        exit( EXIT_FAILURE );
    }

    string_1 = calloc ( sizeof(char * ), MAX_LINES );
    if( ! string_1 )
    {
        perror( "malloc failed" );
        cleanup( file_1, file_2, string_1, string_2 );

        exit( EXIT_FAILURE );
    }


    int i = 0;
    char temp_string[ MAX_LINE_LEN ];

    while ( i<MAX_LINES && fgets(temp_string, sizeof( temp_string ), file_1) )
    {
        string_1[i] = malloc ( MAX_LINE_LEN );
        if( ! string_1[i] )
        {
            perror( "malloc for new line failed" );
            cleanup( file_1, file_2, string_1, string_2 );

            exit( EXIT_FAILURE );
        }

        strcpy (string_1[i], temp_string);
        fputs(string_1[i], stdout);
    }

    printf("\n\n\n\n\n\n\n\n\n\n\n");

    //I do the same for file 2
    i = 0;  // Note: the index into the array needs to be reset

    string_2 = calloc ( sizeof(char *), MAX_LINES );
    if( ! string_2 )
    {
        perror( "malloc failed" );
        cleanup( file_1, file_2, string_1, string_2 );

        exit( EXIT_FAILURE );
    }

    while ( i<MAX_LINES && fgets(temp_string, sizeof( temp_string ), file_2) ) 
    {
        string_2[i] = malloc ( MAX_LINE_LEN );
        if( ! string_2[i] )
        {
            perror( "malloc for new line failed" );
            cleanup( file_1, file_2, string_1, string_2 );

            exit( EXIT_FAILURE );
        }

        strcpy (string_2[i], temp_string);
        fputs(string_2[i], stdout);
    }

    printf("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");

    printf("%s%s%s%s\n\n", string_1[0], string_1[1],string_1[2],string_1[3]);

    printf("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");

    //Here only two lines are printed
    for (size_t i=0; string_1[i]; i++) 
    {
        fputs(string_1[i], stdout);
    }

    printf("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");

    for (size_t i=0; string_2[i]; i++) 
    {
        fputs(string_2[i], stdout);
    }

    cleanup( file_1, file_2, string_1, string_2 );

    system("pause");
    return 0;
}