c - What is the value of number left shift by -1 -

-

this question has answer here:

what result of number when left shifted -1 in c programming using left shift operator?

e.g.: 

23 << -1

from c11 standard 6.5.7p3 (for former versions same):

"if value of right operand negative or greater or equal width of promoted left operand, behavior undefined."

iow: undefined behaviour. prepare nasal demons.

briefly: do not

caution: while many programmers aware of , avoid negative shift counts, ignored counts >= bit-size of value undefined. makes ((unsigned int)1 << 32) - 1 undefined if unsigned int has 32 bits or less. signed values things become more complicated due sign (thanks @chux pointing me @ that). common pitfall. implementations, different results constant expressions (compile-time evaluated) , run-time evaluation might occur.


Comments

Post a Comment

Popular posts from this blog

c - Bitwise operation with (signed) enum value -

-
i using enumerator values flags: typedef enum { = 0x00, b = 0x01u, // u has no influence, expected c = 0x02u, // u has no influence, expected ... } enum_name; volatile unsigned char* reg = someaddress; *reg |= b; according misra-c:2004 bitwise operations shall not done signed type. unfortunately, compiler iar use signed int (or short or char) underlying type of enums, , option can find relates size, not signedness ("--enum-is-int"). according iar c/c++ development guide arm , pages 169 , 211, can define type of enum s if enable iar language extensions ( -e command-line option, or project > options > c/c++ compiler > language > allow iar extensions in ide). in particular, should define "sentinel" value, make sure compiler chooses correct type. prefers signed types, , uses smallest possible integer type, sentinel should largest positive integer corresponding unsigned integer type can describe. example, typedef enum
Read more

xslt - Unnest parent nodes by child node -

-
in xml there items 0-n attributes , item should copied each attribute new item 1 attribute. given xml this: <?xml version="1.0" encoding="utf-8" ?> <items> <item> <name>a</name> <attributes> <attribute> <key>attribute1</key> <value>1</value> </attribute> </attributes> </item> <item> <name>b</name> </item> <item> <name>c</name> <attributes> <attribute> <key>attribute1</key> <value>5</value> </attribute> <attribute> <key>attribute2</key> <value>2</value> </attribute> <attribute> <key>attri
Read more

YouTubePlayerFragment cannot be cast to android.support.v4.app.Fragment -

-
im stuck on 3 days , have tried have come across after lots of searching ,this post last resort, im trying open youtubeplayerfragment using navigation drawer youtubeplayerfragment cannot cast android.support.v4.app.fragment problem edit question : have updated code have used youtubeplayersupportfragment instead of youtubeplayerfragment ,i error in displayview method (case 4: fragment = new youtube(); break;) in main activity saying cannot convert youtube fragment , cannot logcat since cant run it edit question 2: code updated again have runtime problem ,heres logcat 07-22 22:15:09.782: e/androidruntime(20603): fatal exception: main 07-22 22:15:09.782: e/androidruntime(20603): process: net.frankandwalters, pid: 20603 07-22 22:15:09.782: e/androidruntime(20603): java.lang.nullpointerexception: attempt invoke virtual method 'void com.google.android.youtube.player.youtubeplayerview.a()' on null object reference 07-22 22:15:09.782: e/androidruntime(20603): @ com.goog
Read more