How can I get argv as int

Question

i have a piece of code like this    int main  int argc  char  argv          printf   d t   int argv 1       printf   s t   int argv 1        and in shell i do this     test 7  but the first printf result is not 7  how can I get argv   as a int  many thanks

User · Answer

You can use strtol for that   long x  if  argc  lt  2         handle error     x   strtol argv 1   NULL  10     Alternatively  if you re using C99 or better you could explore strtoimax

User · Answer

You can use the function int atoi  const char   str   You need to include  include  lt stdlib h gt  and use the function in this way int x   atoi argv 1    Here more information if needed  atoi - C   Reference

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Basic usage  The  string to long   strtol  function is standard for this   long  can hold numbers much larger than  int    This is how to use it    include  lt stdlib h gt   long arg   strtol argv 1   NULL  10      string to long string  endpointer  base    Since we use the decimal system  base is 10  The endpointer argument will be set to the  first invalid character   i e  the first non-digit  If you don t care  set the argument to NULL instead of passing a pointer  as shown   Error checking  1   If you don t want non-digits to occur  you should make sure it s set to the  null terminator   since a  0 is always the last character of a string in C    include  lt stdlib h gt   char  p  long arg   strtol argv 1    amp p  10   if   p      0      an invalid character was found before the end of the string   Error checking  2   As the man page mentions  you can use errno to check that no errors occurred  in this case overflows or underflows     include  lt stdlib h gt   include  lt errno h gt   char  p  errno   0     not  int errno   because the   include  already defined it long arg   strtol argv 1    amp p  10   if   p      0     errno    0        return 1     In main    returning non-zero means failure       Everything went well  print it as  long decimal  printf   ld   arg     Convert to integer  So now we are stuck with this long  but we often want to work with integers  To convert a long into an int  we should first check that the number is within the limited capacity of an int  To do this  we add a second if-statement  and if it matches  we can just cast it    include  lt stdlib h gt   include  lt errno h gt   include  lt limits h gt   char  p  errno   0     not  int errno   because the   include  already defined it long arg   strtol argv 1    amp p  10   if   p      0     errno    0        return 1     In main    returning non-zero means failure    if  arg  lt  INT MIN    arg  gt  INT MAX        return 1    int arg int   arg      Everything went well  print it as a regular number printf   d   arg int     To see what happens if you don t do this check  test the code without the INT MIN MAX if-statement  You ll see that if you pass a number larger than 2147483647  231   it will overflow and become negative  Or if you pass a number smaller than -2147483648  -231-1   it will underflow and become positive  Values beyond those limits are too large to fit in an integer   Full example   include  lt stdio h gt      for printf    include  lt stdlib h gt     for strtol    include  lt errno h gt      for errno  include  lt limits h gt     for INT MIN and INT MAX  int main int argc  char   argv        char  p      errno   0     not  int errno   because the   include  already defined it     long arg   strtol argv 1    amp p  10       if   p      0     errno    0            return 1     In main    returning non-zero means failure            if  arg  lt  INT MIN    arg  gt  INT MAX            return 1            int arg int   arg          Everything went well  print it as a regular number plus a newline     printf  Your value was   d n   arg int       return 0      In Bash  you can test this with   cc code c -o example    Compile  output to  example    example    2  31-1      Run it echo  exit status         Show the return value  also called  exit status    Using 2  31-1  it should print the number and 0  because 231-1 is just in range  If you pass 2  31 instead  without -1   it will not print the number and the exit status will be 1   Beyond this  you can implement custom checks  test whether the user passed an argument at all  check argc   test whether the number is in the range that you want  etc

User · Answer

Input from command line using atoi  and strtol       include  lt stdio h gt   printf  scanf  include  lt stdlib h gt   atoi  strtol     strtol - converts a string to a long int    atoi - converts string to an int   int main int argc  char  argv          char  p   used in strtol      int i   used in for loop      long int longN   strtol  argv 1   amp p  10       printf  longN    ld n  longN          cast  int  to strtol     int N    int  strtol  argv 1   amp p  10       printf  N    d n  N        int atoiN      for i   0  i  lt  argc  i                    set atoiN equal to the users number in the command line            The C library function int atoi const char  str  converts the string argument str to an integer  type int           atoiN   atoi argv i               printf  atoiN    d n  atoiN         -----------------------------------------------------         Get string input from command line      char   charN       for i   0  i  lt  argc  i                  charN   argv i              printf  charN    s n   charN         Hope this helps  Good luck

User · Answer

argv 1  is a pointer to a string  You can print the string it points to using printf  quot  s n quot   argv 1    To get an integer from a string you have first to convert it  Use strtol to convert a string to an int   include  lt errno h gt       for errno  include  lt limits h gt      for INT MAX  include  lt stdlib h gt      for strtol   char  p  int num   errno   0  long conv   strtol argv 1    amp p  10       Check for errors  e g   the string does not represent an integer    or the integer is larger than int if  errno    0     p      0     conv  gt  INT MAX           Put here the handling of the error  like exiting the program with        an error message   else          No error     num   conv          printf  quot  d n quot   num

[c] How can I get argv[] as int?

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