Delphi Eaccessviolation Error
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Delphi Access Violation
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Access Violation At Address 00000 Read Of Address 00000
only takes a minute: Sign up EAccessviolation AV Error using variables in Private up vote 0 down vote favorite I'm tidying up some code I've been given, for some reason, if the variables are defined under 'Private' (where they need to be to constrain access within this unit). I get EAccessViolation error when writing to them. If I loosely define them access violation at address delphi under Var just before implementaion they can be accessed ok. I'm comparing my structure with other similar units, where the Private units work fine & cant spot any significant differences.. Any suggestions? Error MSG: Project --- raised exception class EAccessViolation Error with message 'access vilation error in module----. Read of address 0000050F interface uses dialogs, math, dateutils, SysUtils, classes; type //double = extended; TDoubleDoubleArray = array of array of double; TSunPositionAlgorithm = class (TObject) private FLocationChanged: boolean; public Constructor Create; Destructor Destroy; procedure SetDefaults; end; Var SunPositionAlgorithm : TSunPositionAlgorithm; F_L0: Double; F_L1: TDoubleDoubleArray; implementation {TSunPositionAlgorithm } constructor TSunPositionAlgorithm.Create; begin SetDefaults; end; procedure TSunPositionAlgorithm.SetDefaults; Begin F_L0:= 1; // works ok FLocationChanged:=true; // throws eaccess violation error End; Calling function (added to Post after David H's 1st question): procedure TSun.NRELPositionOfSun(const DateTime: TDateTime; var Azimuth, Elevation, Declination: double); Var LSunPositionAlgorithm : TSunPositionAlgorithm; Begin LSunPositionAlgorithm := TSunPositionAlgorithm.Create; Try LSunPositionAlgorithm.SetDefaults; blah.. Finally LSunPositionAlgorithm.Destroy; End; End; delphi pascal share|improve this question edited Sep 14 '12 at 10:38 asked Sep 14 '12 at 10:03 SolarBrian 185214 add a comment| 1 Answer 1 active oldest votes u
contain not very accurate phrases. What is an Access Violation Every computer program uses memory for running (*). Memory is consumed by every variable in your program. It can be form, component, object, array, record, string or simple integer. Memory can be allocated automatically for certain types of variables (such as integer or static arrays), the other types require manual control of memory (for example, dynamic arrays). Essentially, from the point of operating system, each variable is characterized by its address (i.e. - location) and size. Roughly speaking, program uses 3 "types" of memory: area for global variables, the stack and the heap. Memory for global variables is allocated by OS loader when http://stackoverflow.com/questions/12422300/eaccessviolation-av-error-using-variables-in-private executable module is loading and it is freed when module is unloading. Global variables are those, which declared outside of class or any routine. The stack is used for allocating memory for local variables (which are declared in some function or procedure) and auxiliary data (such as return addresses or exception handlers). The heap is used for storing dynamic data. Note, that for variables of dynamic types (such as dynamic arrays, strings, objects or components) - though http://eurekalog.blogspot.com/2009/05/access-violation-in-details_12.html the variable itself is stored in global area or stack, but its data is always allocated on the heap and it (often) require manual control. Regardless of who allocates memory for the variable (you, manually or the compiler, automatically), memory for each variable must be allocated before its using, and later (when the variable is no longer needed) it should be freed. Sometimes there can be a situation, where your application trying to get access to certain memory location, which wasn't allocated or was already released - due to bugs in your code. When such things happens - the CPU raises an exception of class EAccessViolation. The usual text for this error is as follows: "Access violation at address XXX in module 'YYY'. Write/read of address ZZZ". Though there is the one simple reason for this kind of error, the real situations for it can be very different. Looking for source code line of Access Violation So, what should you do with access violation? Well, first you should try to identificate a source line in your code, where it appears. If you are getting EAccessViolation while running under debugger: Then you should just click "Break" (it is called "Ok" in older Delphi's versions) and the debugger will point you to source line immediately. Additionally you can take a look at call stack by choosing View/Debug Windows/Call stack from Del
View All Answers My Questions Articles Tutorial Tips, Tricks & Techniques News Database Support Community http://community.embarcadero.com/answers/eaccessviolation-error-when-accessing-server-module-components-through-forms Forums Search Recent DiscussionsResourcesQuality PortalEvents CalendarEmbarcadero on YouTube Job BoardRegistered User DownloadsTrial Downloads Books Login Register HomeAnswersApplication DevelopmentIDEEAccessViolation error when accessing Server Module components through forms. Subscribe via rss or Ask a Question EAccessViolation error when accessing Server Module components through forms. IDE Wednesday, March 09 2016, 07:03 PM Mark Reuben access violation B9919 0 I am developing a datasnap server/client application. I am experiencing problems with my datasnap server, particularly in accessing server module components through forms. For example. My Server Module named as ServerMethods saved as ServerMethodsUnit.pas. I have a TSQLConnection component connected to Interbase in my Server Module named SQLQ_MIS. I have access violation at a main form named FormMain. I have already declared ServerMethodsUnit in my uses clause. Whenever I access ServerMethodsUnit components delphi throws an EAccessViolation error. Is there a proper way to access Server Module components? Tweet Responses (0) Highest Vote Latest Oldest There are no replies here yet. Your Reply Please login to post a reply Share It Answers Categories Uncategorized 86 post(s) Embarcadero 162 post(s) Database 32 post(s) SQL Development13 post(s)Database Administration3 post(s)Data Modeling & Architecture30 post(s) Application Development 197 post(s) IDE167 post(s)Cloud19 post(s)Enterprise20 post(s)Data50 post(s)UI410 post(s) Answers Tags Datasnap delphi seattle 10 Delphi 10 Seattle XE10 delphi XE8 upd1 fireDAC iPhone REST iOS Delphi 10 C++ Rad Studio Berlin VCL Appmethod FMX iOS, Android xe8 Mysql, iOS, Android, firemonkey C++Builder 10.1 Berlin firemonkey Android XE7 bluetooth Delphi 10.1 Berlin Embarcadero Community Website XE6 IDE TListView home company communities partners copyright privacy report software piracy © 2016 Embarcadero Technologies, Inc. All rights reserved.