c - 从顺序文件中选择性地打印行

Question

我可以让我的程序打印出我的文本文件，但我怎样才能让它打印出特定的行呢？就像在几行中有相同的东西并且我希望在运行程序时打印它们？

#include <stdio.h>

int main ( void ){
    static const char filNavn[] = "test.txt";
    FILE *fil = fopen( filNavn, "r" );
    if ( fil != NULL ){
        char line [ 256 ];
        while( fgets( line, sizeof( line ), fil ) != NULL ){
            fputs( line, stdout );
        }
        fclose( fil );
    }
    else{
        perror( filNavn );
    }
    return 0;
}

Answer 1

基本上你需要做的是：

1. 在变量中存储一个插槽line（您所说的 44 个字符）。
2. 使用lib 中的strstr函数查找字符串存在的位置，如果不存在，则返回一个指针。string.hline"2 - 0"NULL
3. 如果指针不是NULL，那么您可以打印该行。

4. 这个循环将一直持续到fil指针到达end of the file.

   if ( fil != NULL ){
   
       /* 44 characters because you said that the data is stored in strings of 44. */
       /* And I will think that you inputed the data correctly. */
       char line [ 44 ];
   
       /* While you don't reach the end of the file. */
       while( !feof( fil ) ){
   
           /* Scans the "slot" of 44 characters (You gave it that format)*/
           /* starting at the position of the pointer fil and stores it in fil*/
           fscanf( fil, %44s, line );
   
           /* If the result of the internal string search (strstr) isn't null. */
           /* Print the line.*/
           if( strstr( line, "2 - 0" ) != NULL ){
               printf( "%s\n", line )
           }
   
           /* Else keep the loop....*/
       }
   
       fclose( fil );
   }
   

Answer 2

只需将您的条件放入读取/打印循环中：

包括

int main ( void )
{
    static const char filNavn[] = "test.txt";
    FILE *fil = fopen( filNavn, "r" );
    if ( fil != NULL )
    {
        char line [ 256 ];
        while( fgets( line, sizeof line, fil ) != NULL )
        {
            // if this line is interesting (eg, has something "the same")
               fputs( line, stdout );
        }
        fclose( fil );
    }
    else
    {
        perror( filNavn );
    }
    return 0;
}