> For the complete documentation index, see [llms.txt](https://calnix.gitbook.io/eth-dev/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://calnix.gitbook.io/eth-dev/compendium/solidity-basics/functions/transaction-vs-call.md).

# Transaction vs Call

There are two ways we can invoke functions.

1. Call
2. Send a transaction (data modification)

![](https://1628544884-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FTgomzlmn9NrxUY0OQ3cD%2Fuploads%2Flp8PfP2p73DMRdcQcsWm%2Fimage.png?alt=media\&token=b1168d74-3e3a-421b-9622-2e03be8c3de9)

{% hint style="info" %}
A transaction is necessary, if a value in a Smart Contract needs to be updated (state change). 

A call is done, if a value is read. 

Transactions cost Ether (gas), need to be mined and therefore take a while until the value is reflected, which you will see later. Calls are virtually free and instant.
{% endhint %}

![transaction followed by call](https://1628544884-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FTgomzlmn9NrxUY0OQ3cD%2Fuploads%2FyNAwT047TE2KzBajKuxS%2Fimage.png?alt=media\&token=f5ac56ad-8dc3-42d8-8c1e-92c9dc5d0fc7)

### Sending a transaction to a function

Anytime we send a transaction to the network it takes time to be process (it must be confirmed by other nodes and mined).

When we send a transaction to a function, we are returned a transaction hash that identifies the transaction. 

* We do not get a return value back, even if the function has a return component in it.
* Costs money.

### Transactions

Transactions always start with an externally owned account signing a transaction and submitting it to the network. The returned value is a transaction receipt. 

The outcome of the transaction is ***unknown*** because nothing has happened yet except that a ***request*** has been submitted to the network for verification ***in the future***.

A typical approach to coping with this fact of life is to wait for the transaction to be mined, then inspect the transaction log for useful output, inspect the success/fail status and draw your own conclusions, or inspect a read-only function to discover the new state after the transaction was mined.