c# create barcode Lesson 4 in .NET

Draw Quick Response Code in .NET Lesson 4

Don't Use _set_se_translator In the first edition of this book, I covered the use of an interesting API named _set_se_translator. It has the magical ability to turn your SEH errors into C++ exceptions by calling a translation function that you define, which simply calls throw on the type you want to use for the conversion. I might as well confess now that although I was well intentioned, my advice was wrong. When you use _set_se_translator, you quickly find out that it doesn't work in release builds. The first problem with _set_se_translator is that it isn't global in scope; it works only on a per-thread basis. That means you probably have to redesign your code to ensure that you call _set_se_translator at the beginning of each thread. Unfortunately, doing that isn't always easy. Additionally, if you're writing a component used by other processes you don't control, using _set_se_translator can and will completely mess up those processes' exception handling if they are expecting SEH exceptions and getting C++ exceptions instead. The bigger problem with _set_se_translator has to do with the arcane implementation details of C++ exception handling. C++ exception handling can be implemented in two ways: asynchronous and synchronous. In asynchronous mode, the code generator assumes that every instruction can throw an exception. In synchronous mode, exceptions are generated explicitly only by a throw statement. The differences between asynchronous and synchronous exception handling don't seem that great, but they certainly are. The drawback of asynchronous exceptions is that the compiler must generate what's called object lifetime tracking code for every function. Since the compiler is assuming that every instruction can throw an exception, every function that puts a C++ class onto the stack has to have code in it to hook up the destructor calls for each object in case an exception is thrown. Since exceptions are supposed to be rare or nearly impossible events, the downside to asynchronous exceptions is that you're paying quite a performance cost for all that object lifetime tracking code you'll never use. Synchronous exception handling, on the other hand, solves the overhead problem by generating the object lifetime tracking code only when a method in the call tree for that method has an explicit throw. In fact, synchronous exception handling is such a good idea that it's the exception type the compiler uses. However, with the compiler assuming that exceptions occur only with an explicit throw in the call stack, the translator function does the throw, which is outside the normal code flow and is thus asynchronous. Consequently your carefully constructed C++ exception wrapper class never gets handled and your application crashes anyway. If you want to experiment with the differences between asynchronous and synchronous exception handling, add /EHa to the compiler command line to turn on asynchronous and remove any /GX or /EHs switches. What makes using _set_se_translator even worse is that it works correctly in debug builds. Only in release builds will you experience the problems. That's because debug builds use synchronous exception handling instead of the release-build default of asynchronous. Because of the inherent problems with _set_se_translator, you'll definitely want to look for it in your code reviews to ensure that no one is using it. 466
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Objective 1.3: Troubleshoot TCP/IP Addressing 13-31
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/username:< username > /password:< password > /domain:< domain > /proxy:< url > /proxyusername:<username> /proxypassword:<password> /proxydomain:< domain >
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On the surface, delegates seem easy to use: you define them by using C# s delegate keyword, you construct instances of them by using the familiar new operator, and you invoke the callback by using the familiar method-call syntax (except instead of a method name, you use the variable that refers to the delegate object) . However, what s really going on is quite a bit more complex than what the earlier examples illustrate . The compilers and the CLR do a lot of behind-the-scenes processing to hide the complexity . In this section, I ll focus on how the compiler and the CLR work together to implement delegates . Having this knowledge will improve your understanding of delegates and will teach you how to use them efficiently and effectively . I ll also touch on some additional features delegates make available . Let s start by reexamining this line of code:
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At this stage, it might be useful to take a quick detour and analyze an attack from a dependency perspective. Earlier we saw what can happen if a malicious removable drive is inserted into a computer. However, it may not be obvious what would happen to the network where that computer lives. Let s assume that the computer in question is domain-joined, as shown in Figure 13-1.
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Sample of C# Code public partial class PasswordCheckTest : System.Web.UI.Page { protected void CheckBoxPassStrengthOn_CheckedChanged(object sender, EventArgs e) { if (CheckBoxPassStrengthOn.Checked) { System.Text.StringBuilder passFunc = new System.Text.StringBuilder(); passFunc.Append("function CheckPassword() {"); passFunc.Append( @"var passLen = document.forms[0].MainContent_ TextBoxPassword.value.length;"); passFunc.Append(@" if (passLen < 4) {"); passFunc.Append(@" document.getElementById(""passwordStrength"")."); passFunc.Append(@"innerText = ""weak"";"); passFunc.Append(@" document.getElementById(""passwordStrength"")."); passFunc.Append(@"style.color = ""red"";}"); passFunc.Append(@" else if (passLen < 6) {"); passFunc.Append(@" document.getElementById(""passwordStrength"")."); passFunc.Append(@"innerText = ""medium"";"); passFunc.Append(@" document.getElementById(""passwordStrength"")."); passFunc.Append(@"style.color = ""blue"";}"); passFunc.Append(@" else if (passLen > 9) {"); passFunc.Append(@" document.getElementById(""passwordStrength"")."); passFunc.Append(@"innerText = ""strong"";"); passFunc.Append(@" document.getElementById(""passwordStrength"")."); passFunc.Append(@"style.color = ""green"";}}"); //register the script Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "CheckPasswordScript", passFunc.ToString(), true); //add an event to the text box to call the script TextBoxPassword.Attributes.Add("onkeyup", "CheckPassword()"); } else { //remove the event from the text box TextBoxPassword.Attributes.Remove("onkeyup"); } } }
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When you compile and execute this code, you get the following output:
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