Reading a string with scanf

Question

I m a little bit confused about something  I was under the impression that the correct way of reading a C string with scanf   went along the lines of   never mind the possible buffer overflow  it s just a simple example   char string 256   scanf    s    string      However  the following seems to work too   scanf    s     amp string      Is this just my compiler  gcc   pure luck  or something else

User · Accepted Answer

An array  decays  into a pointer to its first element  so scanf   s   string  is equivalent to scanf   s    amp string 0    On the other hand  scanf   s    amp string  passes a pointer-to-char 256   but it points to the same place   Then scanf  when processing the tail of its argument list  will try to pull out a char    That s the Right Thing when you ve passed in string or  amp string 0   but when you ve passed in  amp string you re depending on something that the language standard doesn t guarantee  namely that the pointers  amp string and  amp string 0  -- pointers to objects of different types and sizes that start at the same place -- are represented the same way   I don t believe I ve ever encountered a system on which that doesn t work  and in practice you re probably safe  None the less  it s wrong  and it could fail on some platforms   Hypothetical example  a  debugging  implementation that includes type information with every pointer  I think the C implementation on the Symbolics  Lisp Machines  did something like this

User · Answer

I think that this below is accurate and it may help   Feel free to correct it if you find any errors  I m new at C   char str        array of values of type char  with its own address in memory array of values of type char  with its own address in memory as many consecutive addresses as elements in the array including termination null character   0   amp str   amp str 0  and str  all three represent the same location in memory which is address of the first element of the array str  char  strPtr    amp str 0     declaration and initialization   alternatively  you can split this in two    char  strPtr  strPtr    amp str 0      strPtr is a pointer to a char strPtr points at array str strPtr is a variable with its own address in memory strPtr is a variable that stores value of address  amp str 0  strPtr own address in memory is different from the memory address that it stores  address of array in memory a k a  amp str 0    amp strPtr represents the address of strPtr  itself   I think that you could declare a pointer to a pointer as   char   vPtr    amp strPtr      declares and initializes with address of strPtr pointer  Alternatively you could split in two   char   vPtr   vPtr    amp strPtr     vPtr points at strPtr pointer  vPtr is a variable with its own address in memory  vPtr is a variable that stores value of address  amp strPtr final comment   you can not do str    str address is a const   but you can do strPtr

[c] Reading a string with scanf

Examples related to c

Examples related to scanf