how much to malloc for struct stat *

This is a discussion on how much to malloc for struct stat * within the C Programming forums, part of the General Programming Boards category; The following seg faults eventually Code: #include <sys/stat.h> struct stat *fmt; fmt=malloc(sizeof(struct stat *)); do{ if(0!=stat(file,fmt)){ printf("cannot watch the time ...

  1. #1
    Registered User
    Join Date
    Jun 2010
    Posts
    19

    how much to malloc for struct stat *

    The following seg faults eventually

    Code:
    #include <sys/stat.h>
    struct stat *fmt;
    
    fmt=malloc(sizeof(struct stat *));
    do{
      if(0!=stat(file,fmt)){
        printf("cannot watch the time stamp for the journal file\n");
        exit(1);
        }
      if(wait<MAX_WAIT) wait++;
      epoch=fmt->st_mtime;
      } while(old_epoch>epoch);
    free(fmt);
    If I replace the malloc line with

    Code:
    fmt=malloc(100+sizeof(struct stat *));
    seg faults goes away.

    What is the correct way to do this?

    Thanks

  2. #2
    a_capitalist_story
    Join Date
    Dec 2007
    Posts
    2,664
    No need for malloc.

    Code:
    struct stat fmt;
    if (0 != stat(file, &fmt))
    {
       /* Handle error */
    }
    else
      epoch = fmt.st_mtime;

  3. #3
    Registered User
    Join Date
    Jun 2010
    Posts
    19
    That's much better. Thanks.

  4. #4
    C++ Witch laserlight's Avatar
    Join Date
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    Location
    Singapore
    Posts
    23,787
    If you really did want to use malloc, it should be:
    Code:
    fmt = malloc(sizeof(struct stat));
    or better yet:
    Code:
    fmt = malloc(sizeof(*fmt));
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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