Another memory problem

This is a discussion on Another memory problem within the C Programming forums, part of the General Programming Boards category; Ok so occasionally I get a problem and I get a segfault error, and when I check it was with ...

  1. #1
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    Join Date
    Dec 2007
    Posts
    15

    Another memory problem

    Ok so occasionally I get a problem and I get a segfault error, and when I check it was with valgrind I get complain how when I strtok in the assignTemps(string, circuit) function, that string is do invalid reads of 1 byte. I've been looking over the code but I can't find anything wrong. Can someone help me? Thanks.

    Code:
    void getTemperature(Circuit* circuit, char* flp, char* ptrace)
    {
        int osize = 0;
        int size = 0;
        char* string = 0;
        char* overflow = 0;
    
        int status;
        int fd[2];
        int pid;
        int chars_read;
        char buffer[BUFFER];
    
        pipe(fd);
    
        if((pid = fork()) < 0)
        {
             perror("fork");
             exit(-1);
        }
    
        else if(pid == 0)
        {//child
             close(fd[0]);
             dup2(fd[1], STDOUT_FILENO);
    
            execl(hotspotDir, hotspotDir, "-c", "hotspot.config", "-f", flp, "-p", ptrace, (char*)0); 
    	 perror("EXEC!!!!!!!!!!!");
             exit(-1);
        }
        else
        {//parent
             pid = wait(&status);
             close(fd[1]);
    
             chars_read = read(fd[0], buffer, 20);
    
             while((chars_read = read(fd[0], buffer, BUFFER-1)) > 0)
             {
                  buffer[chars_read] = '\0';
                  
                  size = (int)rindex(buffer, '\n') - (int)buffer;
                  if(overflow == 0)
                  {     
                     string = malloc(size+1);
                     string = strncpy(string, buffer, size);
                     size = chars_read - size;
                     if(size != 0)
                     {
                        overflow = malloc(size+1);
                        overflow = strncpy(overflow, rindex(buffer, '\n') + 1, size);
                     }
                     else
                        overflow = 0;
                        
                     osize = strlen(overflow);
                  }
                  else
                  {
                     osize = strlen(overflow);
                     overflow = realloc(overflow, osize + size+1);
                     overflow = strncat(overflow, buffer, size);
                     string = overflow;
                     overflow = malloc(chars_read - size+1);
                     overflow = strncpy(overflow, buffer + size + 1, chars_read - size);
                  }
                  assignTemps(string, circuit);
    
            }
        }
    
    }

  2. #2
    and the hat of wrongness Salem's Avatar
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    rindex returns a pointer, which may be NULL

    So this makes no sense whatsoever
    > size = (int)rindex(buffer, '\n') - (int)buffer;


    > chars_read = read(fd[0], buffer, 20);
    Why do you junk the first 20 chars?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  3. #3
    Registered User
    Join Date
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    15
    >rindex returns a pointer, which may be NULL

    >So this makes no sense whatsoever
    >> size = (int)rindex(buffer, '\n') - (int)buffer;

    buffer always has a newline character so i don't have to worry about that.
    That line pretty much tells me how big the line read in is.


    >> chars_read = read(fd[0], buffer, 20);
    >Why do you junk the first 20 chars?
    This is just header information that I don't care about.

    The weird thing is what that code does works most of the time.

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