Runtime Checking

#disable warning: statement is unreachable +W2111

$ cc +opts warnings_config +wlint -c uninit.c

"uninit.c", line 6: warning #3348-D: declaration hides variable "i" (declared at line 3)

int i;

"uninit.c", line 9: error #2549-D: variable "i" is used before its value is set

if (i) j = 3;

1 error detected in the compilation of "uninit.c".

#pragma diag_suppressdiag_warningdiag_error NNNN #pragma diag_default NNNN

Command line options provide control of diagnostics emission for the entire build or for a specific source file. There are several pragmas which allow the user to control warnings for a specific region within a source file. The use of #pragma diag_suppress disables generation of warning N after the pragma in the source file. The pragma diag_default restores the default handling for diagnostic N. Similarly, diag_warning enables emission of a diagnostic and diag_error converts a warning to an error.

In addition to compile time diagnostics, the HP compilers provide several different +check options to detect some types of errors at runtime.

Advantages of runtime checks in comparison to compile time diagnostics

•Failed runtime checks always indicate a real problem. There are no false positives except for the UMR check (enabled with +check=bounds:pointer +check=uninit).

•Can help detect several hard to catch defects like stack overflow or out-of-bounds accesses that may not be possible with compile time diagnostics.

•Developer does not have to analyze and fix warnings. Action needs to be taken only when a runtime check fails.

Disadvantages of runtime checks

•Runtime checks slow down the user program due to additional instrumentation that is added. In general, they should be used only during development (debug builds) and not for released software (production builds).

•Runtime checks do not cover all paths in the application. Compile time diagnostics can analyze and cover all paths in the source.

•Compile time diagnostics detect problems earlier and with less overhead.

+check=allnoneboundsglobalslockmallocstackthreadtruncateuninit

The +check=xxx options provide runtime checks to detect many common coding errors in the user program. These options introduce additional instructions for runtime checks that may significantly slow down the user program. By default, a failed check will result in the program aborting at the end of execution at runtime. In most cases, an error message and a stack trace will be emitted to stderr before program termination.

The environment variable RTC_NO_ABORT can be set to 0, 1, or 2 to change the behavior of failed runtime check: