--- description: "Learn more about the loop pragma directive in Microsoft C/C++" title: "loop pragma" ms.date: 01/22/2021 f1_keywords: ["loop_CPP", "vc-pragma.loop"] helpviewer_keywords: ["loop pragma", "pragma, loop"] no-loc: ["pragma"] --- # `loop` pragma Controls how loop code is to be considered by the auto-parallelizer, or excludes a loop from consideration by the auto-vectorizer. ## Syntax > **`#pragma loop( hint_parallel(`** *n* **`) )`**\ > **`#pragma loop( no_vector )`**\ > **`#pragma loop( ivdep )`** ### Parameters **`hint_parallel(`** *n* **`)`**\ A hint to the compiler that this loop should be parallelized across *n* threads, where *n* is a positive integer literal or zero. If *n* is zero, the maximum number of threads is used at run time. It's a hint to the compiler, not a command. There's no guarantee that the loop will be parallelized. If the loop has data dependencies, or structural issues, then it won't be parallelized. For example, it isn't parallelized if it stores to a scalar that's used beyond the loop body. The compiler ignores this option unless the [`/Qpar`](../build/reference/qpar-auto-parallelizer.md) compiler switch is specified. **`no_vector`**\ By default, the auto-vectorizer attempts to vectorize all loops that it evaluates may benefit from it. Specify this pragma to disable the auto-vectorizer for the loop that follows. **`ivdep`**\ A hint to the compiler to ignore vector dependencies for this loop. ## Remarks To use the **`loop`** pragma, place it immediately before, not in, a loop definition. The pragma takes effect for the scope of the loop that follows it. You can apply multiple pragma directives to a loop, in any order, but you must state each one in a separate pragma statement. ## See also [Auto-parallelization and auto-vectorization](../parallel/auto-parallelization-and-auto-vectorization.md)\ [Pragma directives and the `__pragma` and `_Pragma` keywords](./pragma-directives-and-the-pragma-keyword.md)