# std::stacktrace_entry::source_line

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< cpp‎ | utility‎ | stacktrace entry

std::uint_least32_t source_line() const; |  | (since C++23)

Returns a 1-based line number that lexically relates to the evaluation represented by *this, or 0 on failure other than allocation failure, e.g. when *this is empty.

Either `source_file` returns the presumed source file name and `source_line` returns the presumed line number, or `source_file` returns the actual source file name and `source_line` returns the actual line number.

### Parameters

(none)

### Return value

The line number specified above on success, 0 on failure other than allocation failure.

### Exceptions

Throws std::bad_alloc if memory for the internal data structures cannot be allocated.

### Notes

The presumed line number is what the predefined macro `__LINE__` expands to, and can be changed by the `#line` directive.

| This section is incomplete Reason: definition of "actual line number" is missing (LWG issue 3507)

This function is not required to be noexcept because getting source line requires allocation on some platforms.

### Example

| This section is incomplete Reason: no example

### See also

line | return the line number represented by this object (public member function of `std::source_location`)

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