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strlcpy (3)
  • >> strlcpy (3) ( FreeBSD man: Библиотечные вызовы )
  • strlcpy (3) ( Linux man: Библиотечные вызовы )

  • BSD mandoc
     

    NAME

    
    
    strlcpy
    
     
    strlcat
    
     - size-bounded string copying and concatenation
    
     
    

    LIBRARY

    Lb libc
    
     
    

    SYNOPSIS

       #include <string.h>
    size_t strlcpy (char *dst const char *src size_t size);
    size_t strlcat (char *dst const char *src size_t size);
     

    DESCRIPTION

    The strlcpy ();
    and strlcat ();
    functions copy and concatenate strings respectively. They are designed to be safer, more consistent, and less error prone replacements for strncpy(3) and strncat(3). Unlike those functions, strlcpy ();
    and strlcat ();
    take the full size of the buffer (not just the length) and guarantee to NUL-terminate the result (as long as Fa size is larger than 0 or, in the case of strlcat (,);
    as long as there is at least one byte free in Fa dst ) . Note that you should include a byte for the NUL in Fa size . Also note that strlcpy ();
    and strlcat ();
    only operate on true ``C'' strings. This means that for strlcpy ();
    Fa src must be NUL-terminated and for strlcat ();
    both Fa src and Fa dst must be NUL-terminated.

    The strlcpy ();
    function copies up to Fa size - 1 characters from the NUL-terminated string Fa src to Fa dst , NUL-terminating the result.

    The strlcat ();
    function appends the NUL-terminated string Fa src to the end of Fa dst . It will append at most Fa size - strlen(dst) - 1 bytes, NUL-terminating the result.  

    RETURN VALUES

    The strlcpy ();
    and strlcat ();
    functions return the total length of the string they tried to create. For strlcpy ();
    that means the length of Fa src . For strlcat ();
    that means the initial length of Fa dst plus the length of Fa src . While this may seem somewhat confusing it was done to make truncation detection simple.

    Note however, that if strlcat ();
    traverses Fa size characters without finding a NUL, the length of the string is considered to be Fa size and the destination string will not be NUL-terminated (since there was no space for the NUL). This keeps strlcat ();
    from running off the end of a string. In practice this should not happen (as it means that either Fa size is incorrect or that Fa dst is not a proper ``C'' string). The check exists to prevent potential security problems in incorrect code.  

    EXAMPLES

    The following code fragment illustrates the simple case:
    char *s, *p, buf[BUFSIZ];
    
    ...
    
    (void)strlcpy(buf, s, sizeof(buf));
    (void)strlcat(buf, p, sizeof(buf));
    

    To detect truncation, perhaps while building a pathname, something like the following might be used:

    char *dir, *file, pname[MAXPATHLEN];
    
    ...
    
    if (strlcpy(pname, dir, sizeof(pname)) >= sizeof(pname))
            goto toolong;
    if (strlcat(pname, file, sizeof(pname)) >= sizeof(pname))
            goto toolong;
    

    Since we know how many characters we copied the first time, we can speed things up a bit by using a copy instead of an append:

    char *dir, *file, pname[MAXPATHLEN];
    size_t n;
    
    ...
    
    n = strlcpy(pname, dir, sizeof(pname));
    if (n >= sizeof(pname))
            goto toolong;
    if (strlcpy(pname + n, file, sizeof(pname) - n) >= sizeof(pname) - n)
            goto toolong;
    

    However, one may question the validity of such optimizations, as they defeat the whole purpose of strlcpy ();
    and strlcat (.);
    As a matter of fact, the first version of this manual page got it wrong.  

    SEE ALSO

    snprintf(3), strncat(3), strncpy(3)  

    HISTORY

    The strlcpy ();
    and strlcat ();
    functions first appeared in Ox 2.4 , and made their appearance in Fx 3.3 .


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    EXAMPLES
    SEE ALSO
    HISTORY


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