c - How to create an input loop? -

i'm looking way write input loop continues print prompts until user enters blank line.

this want do:

loop starts, prints prompt > command line. user enters line ends '\n', program whatever line, , prints > again. continues until user enters blank line (\n), @ point loop terminates.

a simple scanf version can used:

#include <stdio.h>  #define maxl 64  int main (void) {      char str[maxl] = {0};      printf ("\n enter string ([enter] alone quit)\n");      while (printf (" > ") && scanf ("%63[^\n]%*c", str) == 1)     {         /* whatever in code */         printf ("   result: %s\n", str);     }      return 0; } 

use/output

$ ./bin/scanf_enter_quits   enter string ([enter] alone quit)  > string    result: string  >    result:  > 

note: maxl-1 added maximum width specifier scanf prevent write beyond end of array.

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getline example

getline dynamically allocating line buffer allows accept line long want give it. can billions of characters (up extent of memory). strength , weakness. if need limit amount of data accept, check/validate/etc....

#include <stdio.h> #include <stdlib.h>  int main (void) {      char *str = null;     size_t n = 0;     ssize_t nchr = 0;      printf ("\n enter string ([enter] alone quit)\n");      while (printf (" > ") && (nchr = getline (&str, &n, stdin)) > 1)     {         str[--nchr] = 0;                /* strip newline input */         printf ("   (str: %s)\n", str); /* whatever in code */     }      if (str) free (str);      return 0; } 

use/output

$ ./bin/getline_enter_quits   enter string ([enter] alone quit)  > string 1 long want    (str: string 1 long want)  > string 2 make 1000 chars.........................................    (str: string 2 make 1000 chars.........................................)  > 

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scanf dynamic allocation

you can have scanf dynamically allocate space using m conversion specifier (older versions of scanf use a conversion specifier purpose). must provide pointer-to-pointer accept address in case. (e.g. scanf ("%m[^\n]%*c", &str) ).

#include #include

int main (void) {      char *str = null;      printf ("\n enter string ([enter] alone quit)\n");      while (printf (" > ") && scanf ("%m[^\n]%*c", &str) == 1)     {         printf ("   (str: %s)\n", str); /* whatever in code */         if (str) free (str);            /* must free each loop  */         str = null;     }      if (str) free (str);      return 0; } 

use/output

$ ./bin/scanf_dyn_enter_quits   enter string ([enter] alone quit)  > string long want    (str: string long want)  > string length .......... ............. .............    (str: string length .......... ............. .............)  >