examples: don't promote unchecked function calls

[Akim Demaille]

commit 4619b32dc079b7833a784d788114cb1129647723
Author: Akim Demaille <address@hidden>
Date:   Tue May 12 19:03:29 2020 +0200

    examples: don't promote unchecked function calls
    
    * etc/bench.pl.in, examples/c/bistromathic/parse.y,
    * examples/c/calc/calc.y, examples/c/pushcalc/calc.y: Check scanf's
    return value.
    * doc/bison.texi: Likewise, but only for the second example, to avoid
    cluttering the very simple case.

diff --git a/TODO b/TODO
index 006284eb..d8f175f8 100644
--- a/TODO
+++ b/TODO
@@ -7,6 +7,8 @@
 - How about not evaluating incomplete lines when the text is not finished
   (as shells do).
 
+- Caret diagnostics
+
 ** Doc
 *** api.header.include
 
diff --git a/doc/bison.texi b/doc/bison.texi
index 726cbf22..15c9b1c0 100644
--- a/doc/bison.texi
+++ b/doc/bison.texi
@@ -2656,6 +2656,7 @@ found, a pointer to that symbol is returned; otherwise 
zero is returned.
    always succeed, and that integer calculations
    never overflow.  Production-quality code should
    not make these assumptions.  */
+#include <assert.h>
 #include <stdlib.h> /* malloc, realloc. */
 #include <string.h> /* strlen. */
 @end group
@@ -2728,7 +2729,8 @@ yylex (void)
   if (c == '.' || isdigit (c))
     @{
       ungetc (c, stdin);
-      scanf ("%lf", &yylval.NUM);
+      int n = scanf ("%lf", &yylval.NUM);
+      assert (n == 1);
       return NUM;
     @}
 @end group
diff --git a/etc/bench.pl.in b/etc/bench.pl.in
index b7d44f41..036bf52e 100755
--- a/etc/bench.pl.in
+++ b/etc/bench.pl.in
@@ -498,7 +498,8 @@ yylex (void)
     case '5': case '6': case '7': case '8': case '9':
       {
         int nchars = 0;
-        sscanf (input - 1, "%d%n", &yylval.NUM, &nchars);
+        int n = sscanf (input - 1, "%d%n", &yylval.NUM, &nchars);
+        assert (n == 1);
         input += nchars - 1;
         return NUM;
       }
diff --git a/examples/c/bistromathic/parse.y b/examples/c/bistromathic/parse.y
index c2ddb124..78ec6eb7 100644
--- a/examples/c/bistromathic/parse.y
+++ b/examples/c/bistromathic/parse.y
@@ -268,7 +268,8 @@ yylex (const char **line, YYSTYPE *yylval, YYLTYPE *yylloc)
     case '5': case '6': case '7': case '8': case '9':
       {
         int nchars = 0;
-        sscanf (*line - 1, "%lf%n", &yylval->TOK_NUM, &nchars);
+        int n = sscanf (*line - 1, "%lf%n", &yylval->TOK_NUM, &nchars);
+        assert (n == 1);
         *line += nchars - 1;
         yylloc->last_column += nchars - 1;
         return TOK_NUM;
@@ -284,7 +285,8 @@ yylex (const char **line, YYSTYPE *yylval, YYLTYPE *yylloc)
       {
         int nchars = 0;
         char buf[100];
-        sscanf (*line - 1, "%99[a-z]%n", buf, &nchars);
+        int n = sscanf (*line - 1, "%99[a-z]%n", buf, &nchars);
+        assert (n == 1);
         *line += nchars - 1;
         yylloc->last_column += nchars - 1;
         if (strcmp (buf, "exit") == 0)
diff --git a/examples/c/calc/calc.y b/examples/c/calc/calc.y
index 7757648d..ff571114 100644
--- a/examples/c/calc/calc.y
+++ b/examples/c/calc/calc.y
@@ -1,4 +1,5 @@
 %code top {
+  #include <assert.h>
   #include <ctype.h>  /* isdigit. */
   #include <stdio.h>  /* For printf, etc. */
   #include <string.h> /* strcmp. */
@@ -73,7 +74,8 @@ yylex (void)
   if (c == '.' || isdigit (c))
     {
       ungetc (c, stdin);
-      scanf ("%lf", &yylval.NUM);
+      int n = scanf ("%lf", &yylval.NUM);
+      assert (n == 1);
       return NUM;
     }
 
diff --git a/examples/c/pushcalc/calc.y b/examples/c/pushcalc/calc.y
index 7b0b9996..bc27ae95 100644
--- a/examples/c/pushcalc/calc.y
+++ b/examples/c/pushcalc/calc.y
@@ -1,6 +1,6 @@
 %code top {
+  #include <assert.h>
   #include <ctype.h>  /* isdigit. */
-  #include <stdbool.h>
   #include <stdio.h>  /* For printf, etc. */
   #include <string.h> /* strcmp. */
 }
@@ -81,7 +81,8 @@ yylex (YYSTYPE *yylval)
   if (c == '.' || isdigit (c))
     {
       ungetc (c, stdin);
-      scanf ("%lf", &yylval->NUM);
+      int n = scanf ("%lf", &yylval->NUM);
+      assert (n == 1);
       return NUM;
     }