为什么我在 C 中的管道输出仍然产生垃圾数据？

Question

我要做的是运行一个程序并返回整个输出并一次打印一行结果。

当我使用 a.out 作为参数执行程序时，到目前为止一切正常，直到我开始尝试从管道中读取更多数据。我收到以下结果：

Line 0: 
Line 1: 
MCS-51 Family Macro Assembler ASEM-51 V1.3
Line 2:                                   

Line 3: 
a.out(1): illegal character
Line 4:                    
a.out(2): illegal character
Line 5:                    
a.out(3): illegal character
Line 6:                    
a.out(4): illegal character
Line 7:                    
a.out(5): illegal character
Line 8:                    
a.out(5): no END statement found
Line 9:                         

Line 10: 
             6 errors detected
Line 11:                      
Application tried to create a window, but no driver could be loaded.
Line 12:
Make sure that your X server is running and that $DISPLAY is set      correctly.
Line 13:
err:systray:initialize_systray Could not create tray window
Line 14:

但是，第 11 到 14 行根本不应该出现，因为我执行的远程程序在打印第 10 行的内容后完成。

请忽略非法字符语句。这是因为我正在制作一个执行第三方汇编程序的程序，并且我正在传递无效的源代码。

我试图添加一个字符代码 255 以从子级输出回父级，但我无法在父级中接收它，但是如果我尝试在我的系统上执行一个不存在的文件，我会能够将单词“ERROR”发送回父级并在父级中检索它。

我不知道我在这里做错了什么，但我正在尝试找到一种方法来确定何时停止尝试读取更多数据，直到父级从子级接收垃圾而不是真正的输出.

我该如何解决这个问题？

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

char line[100][512];
int numlines=0;

int run(char* dir,char* mainapp,char *par1,char *par2){
int pf[2]; //pf = PipeFields
pipe(pf);
if (fork()==0){
  //CHILD START
  //cmdline = commandline to program = directory (dir) + / + main app name + padded nulls
  char cmdline[10000];
  memset(cmdline,0,10000);
  strcat(cmdline,dir);
  strcat(cmdline,"/");
  strcat(cmdline,mainapp);
  char *args[5]={cmdline,par1,par2,NULL}; //arguments to program
  close(pf[0]);
  //redirect all output streams to same place
  dup2(pf[1],1);
  dup2(pf[1],2);
  //return error as part of output if program can't execute
  if (execve(cmdline,args,NULL) < 0){write(pf[1],"ERROR",5);}
  //return ascii character as last byte to output back to caller
  write(pf[1],(unsigned char*)255,1);
  close(pf[1]);
  //CHILD END
}else{
  //b = buffer
  memset(line,0,51200); //clear all lines of output
  char b[102400];
  memset(b,0,102400); //clear temporary buffer
  char *b2=b; //make reference to buffer for strcat
  char incoming[10001]; //incoming buffer of 10000 bytes of data plus null
  close(pf[1]); //don't need to write to child. close pipe.
  long hasdata=0,sz=0;
  while((sz=read(pf[0],incoming,sizeof(incoming)-1)) > 0){
//execute this while incoming pipe has between 1 and 10000 bytes of data
printf(">>> %ld >> %s\n",sz,incoming); // <-- show output for debugging
incoming[sz]='\0'; //add null to end of incoming data so strcat can work
strcat(b2,incoming); //add incoming data to main buffer
hasdata=1; //we have data
//see if incoming data contains magic character code 255 as a byte
if (strchr(incoming,255)){
  //but this never gets executed? what's going on???
  printf("BREAKKKKK");
  break;
}
  }
  //if theres data then convert it into lines
  if (hasdata==1){
numlines=0; //reset number of lines
char *bp=b; //make reference to data
char *thisln=line[0]; //make reference to line
while(*bp){
  if(*bp=='\n'){ //if theres a new line,...
    numlines++; //increment counter...
    if (numlines > 100){break;} //and exit if theres too many lines
    thisln=line[numlines]; //make reference to next line
  }
  *thisln=*bp; //transfer bytes 1 by 1 to appropiate areas
  bp++;        //and increment pointer
  thisln++;
}
  }
  close(pf[0]);
  }
return 0;
}

int main(int argc,char *argv[]){
  int thisline;
  //get 2 arguments
  if (argc < 2){printf("Filename required\n");return -1;}
  //make sure argument is valid file
  if (access(argv[1],R_OK) < 0){printf("File not found: %s\n",argv[1]);return -2;}
  //run app
  run("/usr/bin","wine","/DOS/8051asm/asemw.exe",argv[1]);
  //print results line by line
  for (thisline=0;thisline<=numlines;thisline++){
printf("Line %d: %s\n",thisline,line[thisline]);
  }
  return 0;
}

Answer 1

下面的代码应该做你想做的。

注意：当 'wine' 不可用时，将输出：

execve failed: No such file or directory

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

#define MAX_LINES    (512)
#define MAX_LINE_LEN (100)

void run(char* mainapp, char *par1, char *par2)
{
    int pf[2]; //pf = PipeFields
    if( pipe(pf) )
    { // then pipe() failed
        perror( "pipe failed" );
        exit( EXIT_FAILURE );
    }

    pid_t pid = fork();
    if( 0 == pid )
    { // child

        //CHILD START
        char *args[]={ mainapp, par1, par2, NULL}; //arguments to program

        close( pf[0] ); // close child output end of pipe
        //redirect all output streams to pipe
        dup2(pf[1],1);
        dup2(pf[1],2);
        close(pf[1]);

        //return error as part of output if program can't execute
        execve(mainapp, args, NULL); // should never return
        perror( "execve failed" );
        exit( EXIT_FAILURE );
    } // end child

    else if (-1 == pid )
    { // error occurred
        perror( "fork failed");
        exit( EXIT_FAILURE );
    } // end fork() error handling

    else
    { // parent
        close( pf[1] ); // close input end of pipe
        size_t thisline;
        char line[ MAX_LINES ][ MAX_LINE_LEN ];
        size_t lineNum=0;
        size_t charNum=0;
        int status;

        memset(line, '\0', MAX_LINES*MAX_LINE_LEN); //clear all lines of output


        while((read(pf[0], &line[lineNum][charNum], 1)) > 0)
        {
            if( '\n' == line[lineNum][charNum] )
            { // then step to next line
                // terminate string
                //charNum++;
                //line[lineNum][charNum] = '\0';
                // init for next line
                lineNum++;
                charNum = 0;
            }

            else
            {
                // step to next char
                charNum++;
            }

            if( charNum >= MAX_LINE_LEN )
            {
                printf( "input line too long -- exiting\n" );
                printf( "%s\n", line[lineNum] );
                wait( &status );
                exit( EXIT_FAILURE );
            }

            if( lineNum >= MAX_LINES )
            {
                printf( "more than %ul lines in file -- exiting\n", MAX_LINES );
                wait( &status );
                exit( EXIT_FAILURE );
            }   
        }
        close( pf[0] ); // close output end of pipe

        //printf( "%lu\n", lineNum); // for testing
        if( strncmp( line[0], "execve", strlen("execve") ) == 0 )
        {
             printf("%s\n", line[thisline]);
        }

        else 
        { // then some data to output
            //print results line by line
            for (thisline=0; thisline<lineNum; thisline++)
            {
                printf("Line %lu: %s\n", thisline, line[thisline]);
            }
        }
    }  // end parent
} // end function: run


int main( int argc, char *argv[] )
{

    if (argc < 2)
    {
        fprintf( stderr, "USAGE: %s <Filename>\n", argv[0]);
        return -1;
    }

    //make sure argument is valid file
    if (access(argv[1],F_OK) < 0)
    {
        perror( "file not found" );
        fprintf( stderr, "Missing file is: %s\n",argv[1]);
        return -2;
    }

    else
    { 
        //run app
        run("/usr/bin/wine", "/DOS/8051asm/asemw.exe", argv[1]);
    }
}