使用 C 打印文本文件的部分

Question

我正在尋找一種解決方案，說明如何僅打印日志文件中的相關部分，我想在其中顯示代碼及其跨越多行的內容。

日志文件的結構如下：

----- start -----
CODE: 1111

DESC: this is some descriptions
      which spans multiple lines.
-----  end  -----

----- start -----
CODE: 2222

DESC: this is some information
      for another code.
-----  end  -----

----- start -----
CODE: 1111

DESC: here is some more info
      for the code again.
-----  end  -----

如果使用 C 解析日志文件以生成與此類似的結果，我想實現什么。

----- start -----
CODE: 1111

DESC: this is some descriptions
      which spans multiple lines.
-----  end  -----

----- start -----
CODE: 1111

DESC: here is some more info
      for the code again.
-----  end  -----

我嘗試了各種 while 循環將文件讀入緩沖區並將字符串與 strstr() 等進行比較，但沒有找到任何適用於我的 if 語句的邏輯。 我曾嘗試探索 fseek()、fgetpos()、fsetpos() 等的使用。我在論壇和博客中搜索了可以幫助我前進但收效甚微的答案。

如果任何閱讀本文的人有分享的解決方案或任何關於我應該如何解決這個問題的指針，或者可以找到此類信息的地方，將不勝感激。

Answer 1

忘記“---開始---”開始。 只需尋找意味着有趣部分開始的目標。 然后 output 直到遇到“---end---”。

這是一個適用於您提供的示例輸入的示例。 只需使用fgets()直到它找到目標字符串，設置一個標志並輸出前導碼（給定）並循環直到它清除標志。 如果當前行既不是開始也不是結束，output（或不是）由標志控制。

您可以通過命令行參數傳遞日志文件名稱和目標字符串來適應您的特定需求。

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

int main() {
    char buf[ 1024 ];

    FILE *ifp = fopen( "log.txt", "rt" );
    if( ifp == NULL )
        exit( EXIT_FAILURE );

    char *target = "CODE: 1111";
    char *start = "-----  start  -----";
    char *end = "-----  end  -----";
    char *blankrow = "";
    bool inRegion = false;

    while( fgets( buf, sizeof buf, ifp ) ) {
        if( inRegion && strncmp( buf, end, strlen( end ) ) == 0 ) {
            inRegion = false;
            printf( "%s", buf );
        } else if( strncmp( buf, target, strlen( target ) ) == 0 ) {
            inRegion = true;
            printf( "%s%s\n%s", blankrow, start, buf );
            blankrow = "\n";
        } else if( inRegion ) {
            printf( "%s", buf );
        }
    }
    fclose( ifp );

    return 0;
}

Answer 2

為了解決問題，你可以閱讀直到遇到該行

----- start -----

然后閱讀下一行，看看它是否包含您要查找的代碼。 如果是，那么你 output 日志條目，如果不是，那么你閱讀並忽略日志條目的 rest。

由於日志條目的末尾清楚地標有該行

-----  end  -----

您可以將日志條目中的每一行與該字符串進行比較。

應該重復這些步驟，直到遇到文件結尾。

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

const char  start_marker[] = "----- start -----";
const char    end_marker[] = "-----  end  -----";
const char target_string[] = "CODE: 1111";

bool read_exactly_one_line( char buffer[], int buffer_size, FILE *fp );

int main( void )
{
    char line[4096];
    bool should_print;

    //read log entries until end-of-file encountered
    for (;;) //infinite loop, equivalent to "while(1)"
    {
        //read until start marker encountered
        for (;;)
        {
           if ( ! read_exactly_one_line( line, sizeof line, stdin ) ) 
            {
                //we are unable to read any further lines due to
                //end-of-file, so we have finished
                exit( EXIT_SUCCESS );
            }

            //determine whether line is empty
            if ( line[0] == '\0' )
                continue;

            //determine whether line is a start marker
            if ( strcmp( line, start_marker ) == 0 )
                break;

            //line is neither empty nor a start marker, which
            //should not occur
            fprintf( stderr, "Parse error: Unexpected input!\n" );
            exit( EXIT_FAILURE );
        }

        //read the line with the code
        if ( ! read_exactly_one_line( line, sizeof line, stdin ) )
        {
            fprintf( stderr, "Error: Encountered end-of-file inside log entry!\n" );
            exit( EXIT_FAILURE );
        }

        //determine whether the line contains the target string
        if ( strcmp( line, target_string ) == 0 )
        {
            //we should print the log entry
            should_print = true;

            //also print the part that we have already read
            printf( "%s\n%s\n", start_marker, line );
        }
        else
        {
            //do not print the remainder of the log entry
            should_print = false;
        }

        //read until end marker
        for (;;)
        {
            if ( ! read_exactly_one_line( line, sizeof line, stdin ) )
            {
                fprintf( stderr, "Error: Encountered end-of-file inside log entry!\n" );
                exit( EXIT_FAILURE );
            }

            //print the line, if appropriate
            if ( should_print )
                printf( "%s\n", line );

            //determine whether line is the end marker
            if ( strcmp( line, end_marker ) == 0 )
            {
                //add one line of spacing between next log entry
                if ( should_print )
                    printf( "\n" );

                //break out of inner infinite loop
                break;
            }
        }
    }
}

//This function will read exactly one line and remove the newline
//character, if it exists. On success, it will return true. If this
//function is unable to read any further lines due to end-of-file,
//it returns false. If it fails for any other reason, it will not
//return, but will print an error message and call "exit" instead.
bool read_exactly_one_line( char buffer[], int buffer_size, FILE *fp )
{
    char *p;

    if ( fgets( buffer, buffer_size, fp ) == NULL )
    {
        if ( ferror( fp ) )
        {
            fprintf( stderr, "Input error!\n" );
            exit( EXIT_FAILURE );
        }

        return false;
    }

    //make sure that line was not too long for input buffer
    p = strchr( buffer, '\n' );
    if ( p == NULL )
    {
        //a missing newline character is ok on end of file
        if ( !feof(fp) )
        {
            fprintf( stderr, "Line was too long for input buffer!\n" );
            exit( EXIT_FAILURE );
        }
    }
    else
    {
        //remove newline character
        *p = '\0';
    }

    return true;
}

使用問題中發布的輸入，該程序具有以下 output：

----- start -----
CODE: 1111

DESC: this is some descriptions
      which spans multiple lines.
-----  end  -----

----- start -----
CODE: 1111

DESC: here is some more info
      for the code again.
-----  end  -----