[ios.openmode]

# 31 Input/output library [[input.output]](./#input.output)

## 31.5 Iostreams base classes [[iostreams.base]](iostreams.base#ios.openmode)

### 31.5.2 Class ios_base [[ios.base]](ios.base#ios.openmode)

#### 31.5.2.2 Types [[ios.types]](ios.types#ios.openmode)

#### 31.5.2.2.4 Type ios_base​::​openmode [ios.openmode]

[🔗](#lib:openmode,ios_base)

`using openmode = T3;
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L1075)

The typeopenmode is a bitmask type ([[bitmask.types]](bitmask.types "16.3.3.3.3 Bitmask types"))[.](#1.sentence-1)

It contains the elements indicated in Table [139](#tab:ios.openmode "Table 139: openmode effects")[.](#1.sentence-2)

Table [139](#tab:ios.openmode) — openmode effects [[tab:ios.openmode]](./tab:ios.openmode)  

| [🔗](#tab:ios.openmode-row-1)<br>**Element** | **Effect(s) if set** |
| --- | --- |
| [🔗](#tab:ios.openmode-row-2)<br>app | seek to end before each write |
| [🔗](#tab:ios.openmode-row-3)<br>ate | open and seek to end immediately after opening |
| [🔗](#tab:ios.openmode-row-4)<br>binary | perform input and output in binary mode (as opposed to text mode) |
| [🔗](#tab:ios.openmode-row-5)<br>in | open for input |
| [🔗](#tab:ios.openmode-row-6)<br>noreplace | open in exclusive mode |
| [🔗](#tab:ios.openmode-row-7)<br>out | open for output |
| [🔗](#tab:ios.openmode-row-8)<br>trunc | truncate an existing stream when opening |