c - 浏览文件行 - C

Question

是否有任何方法可以通过选择上下移动行号而不是按顺序来浏览文件？

到目前为止，我的代码使用 fgets 来获取文件中最后一行 ascii 字符，但通过我的研究，我还没有找到更智能的方式来迭代文件。

例如:

file.txt contains:

"hello\n"
"what's up?\n"
"bye"

我需要能够首先返回“bye”，然后使用按键，打印“what's up\n”，然后通过另一个按键返回“bye”。

Answer 1

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

int main()
{
    FILE *infile;
    char *infile_contents;
    unsigned int infile_size;

    // to read all of the file
    infile = fopen("file.txt", "rb");
    fseek(infile, 0, SEEK_END);
    infile_size = ftell(infile);
    fseek(infile, 0,SEEK_SET);
    infile_contents = malloc(infile_size+1);
    fread(infile_contents, infile_size, 1, infile);
    fclose(infile);
    infile_contents[infile_size]=0;

    // to store the beginning of lines and replace '\n' with '\0'
    size_t num_lines = 1, current_line = 1, length;
    char **lines = malloc(sizeof(char*)), **lines1, *tmp;
    lines[0] = infile_contents;
    while(tmp = strchr(infile_contents, '\n'))
    {
        // to resize lines if it is not big enough
        if(num_lines == current_line)
        {
            lines1 = lines;
            lines = malloc((num_lines<<1)*sizeof(char*));
            memcpy(lines, lines1, num_lines*sizeof(char*));
            memset(lines+num_lines, 0, num_lines*sizeof(char*));
            num_lines <<= 1;
            free(lines1);
        }

        *tmp=0;
        infile_contents = tmp+1;
        lines[current_line++] = infile_contents;
    }

    // to print the lines
    num_lines = current_line-1;
    current_line = num_lines;

    // to skip the last line if it is empty
    if(!lines[current_line][0])
    {
        num_lines--;
        current_line = num_lines;
    }

    while(1)
    {
        printf("%s",lines[current_line]);
        if(getchar())// change to the condition for going down
        {
            if(current_line)
                current_line--;
            else
                current_line=num_lines;
        }
        else
        {
            if(current_line==num_lines)
                current_line=0;
            else
                current_line++;
        }
    }
}