C's string.strchr in TypeScript

How to use

Install via yarn add locutus and import: import { strchr } from 'locutus/c/string/strchr'.

Or with CommonJS: const { strchr } = require('locutus/c/string/strchr')

Use a bundler that supports tree-shaking so you only ship the functions you actually use. Vite, webpack, Rollup, and Parcel all handle this. For server-side use this is less of a concern.

Examples

These examples are extracted from test cases that automatically verify our functions against their native counterparts.

#	code	expected result
1	strchr('Hello, World!', 'o')	'o, World!'
2	strchr('Hello', 'x')	null

C types and TypeScript/JavaScript

C is statically typed while TypeScript/JavaScript is dynamically typed. Locutus C functions accept TypeScript/JavaScript's flexible types but are only parity-verified for inputs that would be valid in C.

For example, abs() in TypeScript/JavaScript accepts floats (like C's fabs()) and handles strings gracefully, but only integer inputs are verified against native C. This pragmatic approach gives you the expected C behavior for valid inputs while leveraging TypeScript/JavaScript's flexibility for edge cases.

Notes

• Returns a pointer to the first occurrence of c in str. In JS, returns the substring starting from the first occurrence, or null.

Here's what our current TypeScript equivalent to C's strchr found in the string.h header file looks like.

TSTypeScript JSJavaScript TSStandalone TS JSStandalone JS

Copy code

export function strchr(str: string, c: string): string | null {
  //  discuss at: https://locutus.io/c/string/strchr/
  // original by: Kevin van Zonneveld (https://kvz.io)
  //      note 1: Returns a pointer to the first occurrence of c in str.
  //      note 1: In JS, returns the substring starting from the first occurrence, or null.
  //   example 1: strchr('Hello, World!', 'o')
  //   returns 1: 'o, World!'
  //   example 2: strchr('Hello', 'x')
  //   returns 2: null

  str = str + ''
  c = (c + '').charAt(0)
  const idx = str.indexOf(c)
  return idx === -1 ? null : str.slice(idx)
}

export function strchr(str, c) {
  //  discuss at: https://locutus.io/c/string/strchr/
  // original by: Kevin van Zonneveld (https://kvz.io)
  //      note 1: Returns a pointer to the first occurrence of c in str.
  //      note 1: In JS, returns the substring starting from the first occurrence, or null.
  //   example 1: strchr('Hello, World!', 'o')
  //   returns 1: 'o, World!'
  //   example 2: strchr('Hello', 'x')
  //   returns 2: null

  str = str + ''
  c = (c + '').charAt(0)
  const idx = str.indexOf(c)
  return idx === -1 ? null : str.slice(idx)
}

Improve this function

Locutus is a community effort following The McDonald's Theory: we ship first iterations, hoping others will improve them. If you see something that could be better, we'd love your contribution.

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Got a rainy Sunday afternoon and a taste for a porting puzzle?

• Get inspiration from the C math.h documentation, the C math.h source.
• Click "New file" in the appropriate folder on GitHub. This will fork the project to your account, directly add the file to it, and send a Pull Request to us.

We will then review it. If it's useful to the project and in line with our contributing guidelines your work will become part of Locutus and you'll be automatically credited in the authors section accordingly.

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