How to iterate over a string in C

Question

Right now I m trying this    include  lt stdio h gt   int main int argc  char  argv           if  argc    3             printf  Usage   s  s sourcecode input   argv 0   argv 1              else           char source      This is an example            int i           for  i   0  i  lt  sizeof source   i                   printf   c   source i                         getchar         return 0      This does also NOT work   char  source    This is an example    int i   for  i   0  i  lt  strlen source   i          printf   c   source i        I get the error     Unhandled exception at 0x5bf714cf  msvcr100d dll  in Test exe  0xC0000005  Access violation while reading at position 0x00000054     loosely translated from german   So what s wrong with my code

User · Answer

This should work    include  lt stdio h gt    include  lt string h gt    int main int argc  char  argv          char  source    This is an example        int length    int strlen source     sizeof source  sizeof char      4 on a 32 bit implementation     for  int i   0  i  lt  length  i                   printf   c   source i

User · Answer

sizeof source  is returning to you the size of a char   not the length of the string  You should be using strlen source   and you should move that out of the loop  or else you ll be recalculating the size of the string every loop  By printing with the  s format modifier  printf is looking for a char   but you re actually passing a char  You should use the  c modifier

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One common idiom is   char  c   source  while   c  putchar  c       A few notes    In C  strings are null-terminated  You iterate while the read character is not the null character   c   increments c and returns the dereferenced old value of c  printf   s   prints a null-terminated string  not a char  This is the cause of your access violation

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The last index of a C-String is always the integer value 0  hence the phrase  null terminated string   Since integer 0 is the same as the Boolean value false in C  you can use that to make a simple while clause for your for loop  When it hits the last index  it will find a zero and equate that to false  ending the for loop   for int i   0  string i   i      printf  Char at position  d is  c n   i  string i

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An optimized approach   for  char character    string  character      0   character      string        putchar character      Do something with character      Most C strings are null-terminated  meaning that as soon as the character becomes a   0  the loop should stop  The    string is moving the pointer one byte  then dereferencing it  and the loop repeats   The reason why this is more efficient than strlen   is because strlen already loops through the string to find the length  so you would effectively be looping twice  one more time than needed  with strlen

User · Answer

sizeof   includes the terminating null character   You should use strlen    but put the call outside the loop and save it in a variable   but that s probably not what s causing the exception  you should use   c   not   s  in printf - you are printing a character  not a string

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Rather than use strlen as suggested above  you can just check for the NULL character    include  lt stdio h gt   int main int argc  char  argv          const char  const pszSource    This is an example        const char  pszChar   pszSource       while  pszChar    NULL  amp  amp   pszChar      0                 printf   s    pszChar             pszChar             getchar         return 0

User · Answer

You want   for  i   0  i  lt  strlen source   i       sizeof gives you the size of the pointer  not the string  However  it would have worked if you had declared the pointer as an array   char source      This is an example      but if you pass the array to function  that too will decay to a pointer  For strings it s best to always use strlen  And note what others have said about changing printf to use  c  And also  taking mmyers comments on efficiency into account  it would be better to move the call to strlen out of the loop   int len   strlen  source    for  i   0  i  lt  len  i       or rewrite the loop   for  i   0  source i     0  i

User · Answer

Just change sizeof with strlen   Like this   char  source    This is an example    int i   for  i   0  i  lt  strlen source   i          printf   c   source i

User · Answer

Replace sizeof with strlen and it should work

User · Answer

sizeof source  returns the number of bytes required by the pointer char   You should replace it with strlen source  which will be the length of the string you re trying to display   Also  you should probably replace printf   s  source i   with printf   c  source i   since you re displaying a character

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You need a pointer to the first char to have an ANSI string    printf   s   source   i     will do the job  Plus  of course you should have meant strlen source   not sizeof source

User · Answer

sizeof source  returns sizeof a pointer as source is declared as char    Correct way to use it is strlen source    Next   printf   s  source i       expects string  i e  s expects string but you are iterating in a loop to print each character  Hence use  c    However your way of accessing iterating  a string using the index i is correct and hence there are no other issues in it

[c] How to iterate over a string in C?

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