64 lines
1.1 KiB
Markdown
64 lines
1.1 KiB
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 num = 27;
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int *ptr_to_num = #
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printf("%i\n", num);
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// 27
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printf("%p\n", ptr_to_num);
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// 0x7ffeb44f7eac
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```
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We indicate that we are creating a pointer with `*`.
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We then retrieve the memory address with `&`.
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We can 'de-reference' back to the value with:
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```c
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printf("%i\n", *ptr_to_num);
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// 27
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```
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## Why are pointers even necessary?
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In other languages you can do something like:
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```js
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let num = 27;
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console.log(num);
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// 27
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function modify(theNumber) {
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theNumber = 28;
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return theNumber;
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}
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```
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In C, you cannot use functions to modify variables that live outside of them
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(e.g. in higher scope).
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If you did the above with C, `num` would still be `27` after the function call.
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This is bcause arguments are passed by value, not by reference to the item in
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memory that the variable refers to.
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So, to modify the actual value in memory, you invoke pointers.
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The above JavaScript in C would be:
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```c
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int num = 27
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int modify(int *the_number) {
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*the_number = 28;
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return the_number;
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}
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```
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