Unterschiede

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--- becki:linux:c [2010-11-08 14:21]
becki
+++ becki:linux:c [2017-12-07 14:19] (aktuell)
becki [Definition of constant Strings]
@@ Zeile 2: / Zeile 2: @@
 This is about ISO C and its standard library. POSIX/Linux enhancements and features are described in [[:becki:my:linux:linux programming]]. How to build applications is described in [[build tools]].
+===== CLI args and main() ==
+<code c>
+int main(int argc, char **argv){
+    char * progName= argv[0]; // Filename of programm itself
+    if (argc >= 2) char * firstArg= argv[1]; // First Argument
+}
+int main(void){}
+// is also possible (Carm p.416)
+// don't omit void! (Carm p.278)
+</code>
+===== C Program Structure ==
+{{page>becki/my/linux/design_blog/2017-01-20_c_program_structure&noheader}}
+===== Position of Pointer Sign ======
+Some investigations:
+<code c>
+int main(int argc, char* argv[]) // Stroustrup p.126
+int main(int argc, char* argv[]) // Josuttis p.21
+int main(int argc, char* argv[], char *env[]) // (!) Breymann p.216
+int main(int argc, char *argv[]) // glibc reference
+int main(int argc, char *argv[]) // Kernighan / Ritchie
+int main(int argc, char *argv[]) // Harbison / Steele
+int main(int argc, char **argv)  // gtk reference
+int main(int argc, char **argv)  // qt reference
+int main(int argc, char **argv)  // fluxbox source
+</code>
+-> I use
+<code c>char *cp</code>
+because
+  - it seems to be more common
+  - declarations like "int a, *ap;" are possible
 ===== Loops ==
@@ Zeile 38: / Zeile 76: @@
 }
 </code>
-===== CLI args and main() ==
-<code c>
-int main(int argc, char **argv){
-    char * progName= argv[0]; // Filename of programm itself
-    if (argc >= 2) char * firstArg= argv[1]; // First Argument
-}
-int main(void){}
-// is also possible (Carm p.416)
-// don't omit void! (Carm p.278)
-</code>
-===== Position of Pointer Sign ======
-Some investigations:
-<code c>
-int main(int argc, char* argv[]) // Stroustrup p.126
-int main(int argc, char* argv[]) // Josuttis p.21
-int main(int argc, char* argv[], char *env[]) // (!) Breymann p.216
-int main(int argc, char *argv[]) // glibc reference
-int main(int argc, char *argv[]) // Kernighan / Ritchie
-int main(int argc, char *argv[]) // Harbison / Steele
-int main(int argc, char **argv)  // gtk reference
-int main(int argc, char **argv)  // qt reference
-int main(int argc, char **argv)  // fluxbox source
-</code>
--> I use
-<code c>char *cp</code>
-because
-  - it seems to be more common
-  - declarations like "int a, *ap;" are possible
 ===== Standard In- and Output ==
@@ Zeile 85: / Zeile 90: @@
 while (fgets(lin, MAX_LINE_LEN, stdin)) {/* do some thing */}
 </code>
+<note tip>If input line lenght is unknown, use ''getline()'' instead of ''fgets()''!
+(See ''freesigs/io_modbus'')</note>
 ''scanf'' can also be used for reading from ''stdin''.
@@ Zeile 103: / Zeile 111: @@
 </code>
-Writing to ''stderr'' is unbuffered, writing to ''stdout'' is buffered ((CARM p.351)) => Always use ''stderr'' for debugging messages ((RRUSP p.68))
+Writing to ''stderr'' is unbuffered, writing to ''stdout'' is buffered ((CARM p.351))
+ ⇒ Always use ''stderr'' for debugging messages ((RRUSP p.68))
 ===== Constants ======
@@ Zeile 212: / Zeile 221: @@
 [static] const char *mystring=  "String" // false, needs 6 Bytes + Pointer
 </code>
   * ''static'' to limit the scope for global strings. Not necessary inside a code block.
   * see also [[http://www.dclc-faq.de/kap2.htm|de.comp.lang.c FAQ]] -> Frage 2.2 / K&R p.101 / Carm p.124
+  * //Writable// strings must be declared as array (eg ''char a[]= "aff";'') not as pointer. See Carm p 32
 === Detailed Description ==
@@ Zeile 374: / Zeile 385: @@
   - Use another, smaller type when space is relevant (eg in ''struct'' definitions or large arrays)
   - Use a bigger type when the space in ''int'' is not sufficient
+===== Private Members in structs ==
+Any pointer type may be an incomplete type. This can be used to get private members in an object:
+==== Library Code ==
+<code c>
+/* file: point-private.h */
+struct point {
+    int x;
+    int y;
+};
+</code>
+<code c>
+/* file: point.c */
+#include <stdlib.h>
+#include "point-private.h"
+struct point * point_new(int x, int y) {
+    struct point *p= malloc(sizeof(struct point));
+    p->x= x;
+    p->y= y;
+    return p;
+}
+int point_get_x(struct point *this) {
+    return this->x;
+}
+</code>
+<code c>
+/* file: point.h */
+struct point * point_new(int x, int y);
+int point_get_x(struct point *this);
+</code>
+==== Client Code ==
+<code c>
+#include <stdio.h>
+#include "point.h"
+int main(void) {
+    struct point *p = point_new(7,4);
+    printf("x=%d\n", point_get_x(p));
+    //printf("x=%d\n", p->x); // Error: incomplete type
+    return 0;
+}
+</code>
 ===== Unsorted Tips ==

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