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+# <small>nlohmann::basic_json::</small>start_pos
+
+```cpp
+#if JSON_DIAGNOSTIC_POSITIONS
+constexpr std::size_t start_pos() const noexcept;
+#endif
+```
+
+Returns the position of the first character in the JSON string from which the value was parsed from.
+
+| JSON type | return value                                   |
+|-----------|------------------------------------------------|
+| object    | position of the opening `{`                    |
+| array     | position of the opening `[`                    |
+| string    | position of the opening `"`                    |
+| number    | position of the first character                |
+| boolean   | position of `t` for `true` and `f` for `false` |
+| null      | position of `n`                                |
+
+## Return value
+
+the position of the first character of the value in the parsed JSON string, if the value was created by the
+[`parse`](parse.md) function, or `std::string::npos` if the value was constructed otherwise
+
+## Exception safety
+
+No-throw guarantee: this member function never throws exceptions.
+
+## Complexity
+
+Constant.
+
+## Notes
+
+!!! note "Note"
+
+    The function is only available if macro [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) has
+    been defined to `#!cpp 1` before including the library header.
+
+!!! warning "Invalidation"
+
+    The returned positions are only valid as long as the JSON value is not changed. The positions are *not* updated
+    when the JSON value is changed.
+
+## Examples
+
+??? example "Example"
+
+    ```cpp
+    --8<-- "examples/diagnostic_positions.cpp"
+    ```
+    
+    Output:
+
+    ```
+    --8<-- "examples/diagnostic_positions.output"
+    ```
+
+    The output shows the start/end positions of all the objects and fields in the JSON string.
+
+## See also
+
+- [end_pos](end_pos.md) to access the end position
+- [JSON_DIAGNOSTIC_POSITIONS](../macros/json_diagnostic_positions.md) for an overview of the diagnostic positions
+
+## Version history
+
+- Added in version 3.12.0.