39 lines
776 B
Markdown
39 lines
776 B
Markdown
---
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tags:
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- C
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---
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A pointer is a reference to the address of a variable in memory.
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```c
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int x = 27;
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int *ptr = &x;
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printf("%i\n", x);
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// 27
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printf("%p\n", *ptr);
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// 0x7ffeb44f7eac
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```
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The `&` and `*` is frankly confusing.
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In the previous example, `int *ptr = &x`, `ptr` is a variable that holds the
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memory address of `x`. `*` signals that it is a pointer variable, `&` is what
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does the retrieval.
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In the following:
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```c
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int x = 27;
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int *ptr = &x;
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int value = *ptr;
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```
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We again set `ptr` to the memory address of `x`, but we use `*` on the last line
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to **de-reference** the pointer and get the original value back. Thus `value`
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becomes equal to `27`.
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Pointers are necessary because C uses a [call by value](./C_is_call_by_value.md)
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system for function arguments.
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