复制文件跳过前n行和后m行 [英] Copy file skipping first n lines and last m lines

问题描述

我想复制一个文件，跳过其前n行，最后m行使用open，read，write和lseek
（例如n = 1，m = 2，源文件：

AAAAAAA

BBBBBBB

CCCCCCC

DDDDDDD

dest文件：
BBBBBBB）

我知道如何复制文件，但不知道如何跳过这些行。这里是我的复制代码：

  char buf [128]; 
 size_t size; 
 
 int source = open（argv [1]，O_RDONLY）; 
 int dest = open（argv [2]，O_CREAT | O_APPEND | O_WRONLY）; 
 
 if（source == -1）{
 printf（error）; 
 return; 
} 
 if（dest == -1）{
 printf（error）; 
 return; （（size = read（source，buf，sizeof（buf）））> 0）{
 write（dest，buf，size）; 
} 
 
。 
} 
 
 close（source）; 
 close（dest）; 
  

如何解决这个问题？

fgets 来读取您的文件，因为它会一行一行地读取它。

因为要说总共有多少行，我建议你

• 使用 fgets 逐行读取文件
  
• 跳过输出第一个 n 行
li>

• 将其余的写入输出文件并计算行数并记住每行的长度。 使用 ftruncate
code>截断最后一个 m 行。






应该做的伎俩：

$ $ p $ code void copy_nm（char * source，char * dest，int n，int m）{
FILE * in = fopen（source，r）;
FILE * out = fopen（dest，w）;

size_t file_length = 0;
size_t line_lengths [m + 1];
memset（line_lengths，0，sizeof（line_lengths））;

int lengths_iterator = 0;


char buffer [0x400];

while（fgets（buffer，sizeof（buffer），in））{
size_t length = strlen（buffer）;

if（n）{//跳过这一行
if（buffer [length - 1] =='\\\
'）//仅当它是一个实线时
-
继续;
}

fwrite（buffer，length，1，out）;
line_lengths [lengths_iterator] + =长度;
file_length + = length;

if（buffer [length - 1]！='\\\
'）{//行长于缓冲区
continue;
}

lengths_iterator ++;
lengths_iterator％= m + 1;

line_lengths [lengths_iterator] = 0;


for（lengths_iterator = 0; lengths_iterator< m + 1; lengths_iterator ++）{
file_length - = line_lengths [lengths_iterator];
}

fseek（out，0，SEEK_SET）; //在截断
之前回滚ftruncate（fileno（out），file_length）;

}


I want to copy a file with skipping first n of its lines and last m lines using open, read, write and lseek (eg. n = 1, m = 2, source file:
AAAAAAA
BBBBBBB
CCCCCCC
DDDDDDD

dest file:
BBBBBBB )

I know how to copy a file but don't know how to skip the lines. Here is my code for copy:

    char buf[128];
    size_t size;

    int source = open(argv[1], O_RDONLY);
    int dest = open(argv[2], O_CREAT | O_APPEND | O_WRONLY);

    if(source == -1) {
            printf("error");
            return;
    }
    if(dest == -1) {
            printf("error");
            return;
    }

    while((size = read(source, buf, sizeof(buf))) > 0) {
            write(dest, buf, size);
    }

    close(source);
    close(dest);

How can i solve this problem?

解决方案

You should use fgets to read your file since that will read it line by line.

Because it is not trivial to say how many lines you have in total I would suggest you

• use fgets to read the file line by line
• skip outputting the first n lines
• write the rest to your output files and count the number of lines and remember the length of each.
• use ftruncate to truncate off the last m lines.

This should do the trick:

void copy_nm(char * source, char * dest, int n, int m) {
    FILE * in = fopen(source, "r");
    FILE * out = fopen(dest, "w");

    size_t file_length = 0;
    size_t line_lengths[m + 1];
    memset(line_lengths, 0 , sizeof(line_lengths));

    int lengths_iterator = 0;


    char buffer[0x400];

    while (fgets(buffer, sizeof(buffer), in)) {
        size_t length = strlen(buffer);

        if (n) { // skip this line
            if (buffer[length - 1] == '\n') // only if it is a real line
                n--;
            continue;
        }

        fwrite(buffer, length, 1, out);
        line_lengths[lengths_iterator] += length;
        file_length += length;

        if (buffer[length - 1] != '\n') { // line was longer then the buffer
            continue;
        }

        lengths_iterator++;
        lengths_iterator %= m+1;

        line_lengths[lengths_iterator] = 0;
    }

    for (lengths_iterator = 0; lengths_iterator < m+1; lengths_iterator++) {
        file_length -= line_lengths[lengths_iterator];
    }

    fseek(out, 0, SEEK_SET); // rewind before truncating
    ftruncate(fileno(out), file_length);

}

这篇关于复制文件跳过前n行和后m行的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！