Problem with strcat()

This is a discussion on Problem with strcat() within the C Programming forums, part of the General Programming Boards category; What's wrong with my functions ? I need to check if the files found are dirs! but when a use ...

  1. #1
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    Problem with strcat()

    What's wrong with my functions ? I need to check if the files found are dirs! but when a use strcat() for sum de localdir and the name.... puff !! segment fault !!! thanks

    Code:
    void scan (char *localDir) {
        struct dirent **namelist;
        int n;
        n = scandir(localDir, &namelist, 0, alphasort);
        if (n < 0)
            perror("scandir");
        else {
            while(n--) {
    	    char *filename = strcat(localDir, namelist[n]->d_name);
    	    if (isDir(filename) {
                        printf("%s \n", filename);
    	    }
                free(namelist[n]);
            }
            free(namelist);
        }
    
    }

  2. #2
    and the hat of wrongness Salem's Avatar
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    Say you have
    .
    ..
    foo.dat
    bar.txt

    > char *filename = strcat(localDir, namelist[n]->d_name);
    localDir is going to end up being one long long string of
    ...foo.datbar.txt

    Are you sure it's
    a) what you wanted to do
    b) long enough
    c) initialised with a suitable \0 ending string to begin with.
    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.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  3. #3
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    Salem,

    I need to check if the found files are a directories.. is simple. but I am never coder C before.
    I can make the software print the file names on the screen... but, I need use, something like strcat(), for union DIRNAME (where scandir() search files) and the FILENAMES (namelist[n]->d_name). So, I can check with:
    isDir(filename) !
    thanks for your help

  4. #4
    and the hat of wrongness Salem's Avatar
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    What's wrong with
    isDir(namelist[n]->d_name)
    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.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  5. #5
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    if I am not on the current dir ? ...namelist[n]->d_name is just the file name
    Last edited by souza; 11-09-2008 at 12:57 PM.

  6. #6
    and the hat of wrongness Salem's Avatar
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    So you really want to create
    mydir/.
    mydir/..
    mydir/foo.dat
    mydir/bar.txt

    Perhaps something along these lines, inside the loop
    char temp[size]; // you pick a size
    strcpy( temp, dir );
    strcat( temp, file );
    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.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  7. #7
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    thats it !! thanks a lot Salem.
    I dont know why, but strcpy() save my code !

    cya

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