pragma

问题 I've recently found the CHANGES() function available inside of SQLite. I'm doing something like the following inside of my Android code: db.execSQL(sqlStatement, argumentArray); int result; SQLiteStatement stmt = db.compileStatement("SELECT CHANGES()"); try { return stmt.simpleQueryForLong(); } finally { stmt.close(); } What I'm seeing that I get good data for all statements such as: UPDATE `footable` SET `stuff` = 'fepojefpjo' (returns 1 row updated) DROP TABLE `footable` (returns 2 rows

问题 I am trying to align data members by using #pragma pack (n). Take the following as an example: #include <iostream> using namespace std; #pragma pack(8) // or (16) struct A { int a; char b; char c; char d; char e; char f; double g; }; int main() { cout << sizeof(A) << endl; return 0; } Both will print 24 for #pragma pack(8) and #pragma pack(16) . I can understand the result for n=8 with the data alignment, of my understanding, as follows: Bytes: |1 2 3 4|5|6|7|8|9|10 11 12 13 14 15 16|17 18 19

问题 I'm debugging a perl script which looks like this (simplified): #!/usr/bin/perl use strict; use warnings; use Evil::Module; printf "%.3f\n", 0.1; This script outputs 0,100 (note , instead of . ). If I comment out the use Evil::Module statement, the output will be 0.100 . I believe that this is related to locale setting in the module. But locale is a lexical pragma (according to the manpage), and it's not used within the script. What's happening here? 回答1: The use locale pragma is lexical, but

问题 I'm trying to interface with Ada code using C++, so I'm defining a struct using bit fields, so that all the data is in the same place in both languages. The following is not precisely what I'm doing, but outlines the problem. The following is also a console application in VS2008, but that's not super relevant. using namespace System; int main() { int array1[2] = {0, 0}; int *array2 = new int[2](); array2[0] = 0; array2[1] = 0; #pragma pack(1) struct testStruct { // Word 0 (desired) unsigned a

问题 Errors: E/Database( 8614): Failure 21 (out of memory) on 0x0 when preparing 'PRAGMA user_version = 1'. E/Database( 8614): Failure 21 (out of memory) on 0x0 when preparing 'ROLLBACK;'. D/Database( 8614): exception during rollback, maybe the DB previously performed an auto-rollback D/AndroidRuntime( 8614): Shutting down VM W/dalvikvm( 8614): threadid=3: thread exiting with uncaught exception (group=0x4001dc20) E/AndroidRuntime( 8614): Uncaught handler: thread main exiting due to uncaught

问题 All of my header files use include guards as well as pragma once : #pragma once #ifndef FILE_NAME_H #define FILE_NAME_H class foo { //foo interface.. }; #endif /* FILE_NAME_H */ I understand that pragma once is not standard and may not be the same across compilers, but is there any chance it will cause and error? Would it be better to somehow test if it's available first? #ifdef THIS_COMPILER_SUPPORTS_PRAGMA_ONCE #pragma once #endif #ifndef FILE_NAME_H #define FILE_NAME_H class foo { //foo

问题 What is the scope of a pragma directive? For example, if I say #pragma warning(disable: 4996) in a header file A that is included from a different file B, will that also disable all those warnings inside B? Or should I enable the warning at the end of file A again? 回答1: It is till the end of the translation unit. Informally, a TU is the source file with its include files. The usual pattern is this: #pragma warning (push) //save #pragma warning (disable: xxxx) #pragma warning (disable: yyyy) .

问题 When I use the flash.data routines to issue a SQLite "PRAGMA encoding" statement, I get an error suggesting that this isn't supported: 'Error #3115: SQL Error.', details:'PRAGMA is not allowed in SQL.', operation:'execute', detailID:'2005 Is there a workaround? 回答1: In a word no. See for supported and unsupported features. http://help.adobe.com/en_US/as3/dev/WSd47bd22bdd97276f1365b8c112629d7c47c-8000.html#WSd47bd22bdd97276f-5741a41a1262b2de46b-8000. However on that page however you will see..

问题 I'm looking for a pragma I can use to hide the compiler warning generated when a field used in the WHERE condition of a select may contain NULL values in the database. Having read SAP note 1088403, I am aware of the possible issues here but I cannot apply the solutions suggested there since I'm using a range, not a single value in the WHERE clause. In either case this is legacy code that was never found to be defective (as far as we know) and will be replaced before long. However while I'm

问题 What's Clang's equivalent to #pragma message as used in GCC and MSVC? 回答1: I've brought this up on the Clang mailing list, and it's in discussion now. It's subsequently been implemented as a warning, and hopefully soon it will be behave as it does in other compilers. 回答2: #pragma message has been implemented recently - too recently for the current release (2.7), but it should be included in the forthcoming 2.8. 来源： https://stackoverflow.com/questions/3796894/pragma-message-in-clang