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--- system-programming:fgets [2024/04/19 18:02] – ایجاد شد pejman
+++ system-programming:fgets [2024/06/18 01:22] (فعلی) – حذف شد pejman
@@ خط 1: / خط 1: @@
-====== تابع ()fgets - خواندن از stdin به شکل pipe-friendly ======
-----
-==== Section 1 ====
-<code C>
-// man 3 fgets
-/* fgets()  reads  in  at  most one less than size characters from stream and stores them into the
- * buffer pointed to by s.  Reading stops after an EOF or a newline.  If a newline is read, it  is
- * stored  into  the buffer.  A terminating null byte ('\0') is stored after the last character in
- * the buffer.
- * fgets() returns s on success, and NULL on error or when end of file occurs while no  characters
- * have been read.
- */
-#include <stdio.h>
-char *fgets(char *s, int size, FILE *stream);
-// man 3 memset
-/* memset - fills the first n bytes of the memory area pointed to by s with the constant byte c */
-#include <string.h>
-void *memset(void s[.n], int c, size_t n);
-</code>
-<code C>
-/* case-changer.c */
-#include <stdio.h>
-#include <string.h>
-int main(void)
-{
-    char c[20] = { 0 };
-    char newcase[20] = { 0 };
-    int i;
-    while(fgets(c, sizeof(c), stdin) != NULL)
-    {
-        for(i=0; i<=sizeof(c); i++)
-        {
-            /* Upper case to lower case */
-            if ( (c[i] >= 65) && (c[i] <= 90) )
-            {
-                newcase[i] = c[i] + 32;
-            }
-            /* Lower case to upper case */
-            if ( (c[i] >= 97 && c[i] <= 122) )
-            {
-                newcase[i] = c[i] - 32;
-            }
-        }
-        printf("%s\n", newcase);
-        /* zero out the arrays so there are no
-           left-overs in the next run */
-        memset(c, 0, sizeof(c));
-        memset(newcase, 0, sizeof(newcase));
-    }
-    return 0;
-}
-</code>
-  $ make case-changer
-  cc     case-changer.c   -o case-changer
-  $ ./case-changer
-  hello
-  HELLO
-  AbCdEf
-  aBcDeF
-  $ ls / | head -n 5 | ./case-changer
-  BIN
-  BOOT
-  COMMAND
-  DEV
-  ETC
-  $ man ls | egrep '^[A-Z]+$' | ./case-changer
-  name
-  synopsis
-  description
-  author
-  copyright
-<code C>
-/* ascii-table.c */
-#include <stdio.h>
-int main(void)
-{
-    char c;
-    for (c = 65; c<=90; c++)
-    {
-        printf("%c = %d    ", c, c); /* upper case */
-        printf("%c = %d\n", c+32, c+32); /* lower case */
-    }
-    return 0;
-}
-</code>
-  $ make ascii-table
-  cc     ascii-table.c   -o ascii-table
-  $ ./ascii-table
-  A = 65    a = 97
-  B = 66    b = 98
-  C = 67    c = 99
-  D = 68    d = 100
-  E = 69    e = 101
-  F = 70    f = 102
-  G = 71    g = 103
-  H = 72    h = 104
-  I = 73    i = 105
-  J = 74    j = 106
-  K = 75    k = 107
-  L = 76    l = 108
-  M = 77    m = 109
-  N = 78    n = 110
-  O = 79    o = 111
-  P = 80    p = 112
-  Q = 81    q = 113
-  R = 82    r = 114
-  S = 83    s = 115
-  T = 84    t = 116
-  U = 85    u = 117
-  V = 86    v = 118
-  W = 87    w = 119
-  X = 88    x = 120
-  Y = 89    y = 121
-  Z = 90    z = 122
-----
-==== Section 2 ====
-<code C>
-// man 3 strspn
-/* The  strspn()  function  returns  the number of bytes in the initial segment of s which consist
- * only of bytes from accept.
- */
-#include <string.h>
-size_t strspn(const char *s, const char *accept);
-// man 3 strlen
-/* The strlen() function calculates the length of the string pointed to by s, excluding the
- * terminating null byte ('\0').
- */
-#include <string.h>
-size_t strlen(const char *s);
-</code>
-<code C>
-/* mph-to-kph.c */
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-int main(void)
-{
-    char mph[10] = { 0 };
-    while(fgets(mph, sizeof(mph), stdin) != NULL)
-    {
-        /* Check if mph is numeric
-         * (and do conversion) */
-        if( strspn(mph, "0123456789.-\n") ==
-            strlen(mph) )
-        {
-            printf("%.1f\n", (atof(mph)*1.60934) );
-        }
-        /* If mph is NOT numeric, print error
-         * and return */
-        else
-        {
-            fprintf(stderr, "Found non-numeric"
-                " value\n");
-            return 1;
-        }
-    }
-    return 0;
-}
-</code>
-  $ make mph-to-kph
-  cc     mph-to-kph.c   -o mph-to-kph
-  $ ./mph-to-kph
-.5
-.6
-.9
-  hello
-  Found non-numeric value
-  $ echo $?
-  $ ./mph-to-kph
-.5
-  <ctrl-D>
-  $ echo $?
-  $ cat avg.txt
--minute average: 61 mph
--minute average: 55 mph
--minute average: 54 mph
--minute average: 52 mph
--minute average: 52 mph
--minute average: nn mph
-  $ awk '{print $3}' avg.txt
-  nn
-  $ awk '{print $3}' avg.txt  | ./mph-to-kph
-.2
-.5
-.9
-.7
-.7
-  Found non-numeric value
-  $ awk '{print $3}' avg.txt  | ./mph-to-kph  2> /dev/null | sed -e 's,$, km/h,'
-.2 km/h
-.5 km/h
-.9 km/h
-.7 km/h
-.7 km/h
-----
-==== Section 3 ====
-<code C>
-/* mph-to-kph_v2.c */
-#define _XOPEN_SOURCE 500
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
-void printHelp(FILE *stream, char progname[]);
-int main(int argc, char *argv[])
-{
-   char mph[10] = { 0 };
-   int opt;
-   int cont = 0;
-   /* Parse command-line options */
-   while ((opt = getopt(argc, argv, "ch")) != -1)
-   {
-      switch(opt)
-      {
-         case 'h':
-            printHelp(stdout, argv[0]);
-            return 0;
-         case 'c':
-            cont = 1;
-            break;
-         default:
-            printHelp(stderr, argv[0]);
-            return 1;
-      }
-   }
-   while(fgets(mph, sizeof(mph), stdin) != NULL)
-   {
-      /* Check if mph is numeric
-       * (and do conversion) */
-      if( strspn(mph, "0123456789.-\n") ==
-            strlen(mph) )
-      {
-         printf("%.1f\n", (atof(mph)*1.60934) );
-      }
-      /* If mph is NOT numeric, print error
-       * and return */
-      else
-      {
-         fprintf(stderr, "Found non-numeric "
-            "value\n");
-         if (cont == 1) /* Check if -c is set */
-         {
-            continue; /* Skip and continue if
-                       * -c is set */
-         }
-         else
-         {
-            return 1; /* Abort if -c is not set */
-         }
-      }
-   }
-   return 0;
-}
-void printHelp(FILE *stream, char progname[])
-{
-   fprintf(stream, "%s [-c] [-h]\n", progname);
-   fprintf(stream, " -c continues even though a non"
-      "-numeric value was detected in the input\n"
-      " -h print help\n");
-}
-</code>
-  $ make mph-to-kph_v2
-  cc     mph-to-kph_v2.c   -o mph-to-kph_v2
-  $ ./mph-to-kph_v2
-.6
-.4
-  hello
-  Found non-numeric value
-  $ ./mph-to-kph_v2  -c
-.5
-.8
-  hello
-  Found non-numeric value
-.1
-.2
-  <ctrl-d>
-  $ cat avg-with-garbage.txt
--minute average: 61 mph
--minute average: 55 mph
--minute average: 54 mph
--minute average: 52 mph
--minute average: 52 mph
--minute average: nn mph
--minute average: 49 mph
--minute average: 47 mph
--minute average: nn mph
-  error reading data from interface
--minute average: 43 mph
-  $ awk '{print $3}' avg-with-garbage.txt
-  nn
-  nn
-  data
-  $ awk '{print $3}' avg-with-garbage.txt | ./mph-to-kph_v2 -c
-.2
-.5
-.9
-.7
-.7
-  Found non-numeric value
-.9
-.6
-  Found non-numeric value
-  Found non-numeric value
-.2
-  $ awk '{print $3}' avg-with-garbage.txt | ./mph-to-kph_v2 -c 2> errors.txt 1> output.txt
-  $ cat output.txt
-.2
-.5
-.9
-.7
-.7
-.9
-.6
-.2
-  $ cat errors.txt
-  Found non-numeric value
-  Found non-numeric value
-  Found non-numeric value