Error map
Array to string conversion Warning: Array to string conversion
PHP · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (12). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (12)
Deprecated: Implicit conversion from float 2.5 to int loses precision
PHP 8.1+ warns when a float with a fractional part is silently converted to int (array keys, % operator, int parameters).
System.InvalidCastException: Unable to cast object of type 'X' to type 'Y'
An explicit cast failed because the object’s runtime type isn’t the target type.
Fatal error: Uncaught TypeError: foo(): Argument #1 ($x) must be of type int, string given
A function received a value of the wrong type for a typed parameter.
Warning: Undefined variable $x
PHP read a variable that was never assigned in the current scope.
Swift: Cannot convert value of type 'X' to expected argument type 'Y'
The value’s type doesn’t match what the function or property expects.
TS2564: Property 'x' has no initializer and is not definitely assigned in the constructor
With strictPropertyInitialization on, a class property declared without ? or a default isn’t set in the constructor.
Fatal error: Uncaught TypeError: Unsupported operand types: string + int
An arithmetic or array operator was used with incompatible types (PHP 8 is stricter than PHP 7).
FastCGI sent in stderr: "Primary script unknown"
Nginx passed a script path to PHP-FPM that PHP-FPM couldn’t find — usually a wrong SCRIPT_FILENAME or root.
java.lang.ClassCastException: class A cannot be cast to class B
An object was cast to a type it isn’t.
Composer: PHP Fatal error: Allowed memory size of 1610612736 bytes exhausted
Composer ran out of memory while resolving or installing dependencies.
Fatal error: Uncaught Error: Cannot use object of type stdClass as array
Code used array syntax (`$x['key']`) on an object.
Rust: error[E0308]: mismatched types — expected `X`, found `Y`
A value’s type doesn’t match what the context expects — common with &str vs String, Option/Result vs plain values, and integer ty…
Two steps away (35)
DeprecationWarning: Buffer() is deprecated due to security and usability issues (DEP0005)
Code (yours or a dependency) uses the deprecated new Buffer() constructor.
Deprecated: strlen(): Passing null to parameter #1 ($string) of type string is deprecated
PHP 8.1+ warns when null is passed to a built-in function that expects a string/int.
Deprecated: Creation of dynamic property Foo::$bar is deprecated
PHP 8.2+ deprecates creating properties that aren’t declared in the class.
AttributeError: 'X' object has no attribute 'y'
You accessed an attribute or method that doesn’t exist on that object type.
java.lang.IllegalArgumentException
A method rejected an argument value as invalid.
java.lang.IllegalStateException
A method was called when the object wasn’t in the right state for it.
PHP Fatal error: Allowed memory size of X bytes exhausted
The script tried to use more memory than PHP’s `memory_limit` allows.
PHP Fatal error: Uncaught Error: Call to undefined function
PHP can’t find the function you called — usually a missing extension, missing include, or namespace issue.
Fatal error: Cannot redeclare function foo() (previously declared in …)
The same function (or class) was defined twice — usually a file included more than once.
TypeError: Cannot read properties of undefined (reading 'x')
You tried to access a property on a value that is `undefined` (or `null`) — usually data that hasn’t loaded yet or a wrong proper…
TypeError: Cannot set properties of undefined (setting 'x')
Code assigned a property on a value that is undefined (or null).
TypeError: Cannot convert undefined or null to object
Object.keys/entries/assign was called with undefined or null.
TS7016: Could not find a declaration file for module 'x'. 'x.js' implicitly has an 'any' type.
The JavaScript package has no TypeScript types bundled and no @types package installed.
TS2304: Cannot find name 'x'.
TypeScript doesn’t know an identifier — a missing import, missing type definitions (e.g. for Node or Jest globals), or a typo.
TS2339: Property 'x' does not exist on type 'Y'.
TypeScript’s type for the object doesn’t include that property.
TypeError: x is not a constructor
new was used with something that isn’t a class/constructor — usually a wrong import.
TS2345: Argument of type 'string | undefined' is not assignable to parameter of type 'string'.
A value’s type doesn’t match the function parameter — commonly a possibly-undefined value passed where a definite one is required.
TypeError: unsupported operand type(s) for +: 'int' and 'str'
An operator was used between two incompatible types, such as adding a number to a string.
WordPress on PHP 8: Fatal error: Uncaught Error: Call to undefined function create_function() / each()
An old plugin/theme uses functions removed in PHP 8 (create_function, each), so the site breaks after a PHP upgrade.
TS2322: Type 'X' is not assignable to type 'Y'
You assigned a value whose type doesn’t match the declared type of the variable, property or return value.
HTTP 403 Forbidden
The server understood the request but refuses to authorize it — you (or the server process) are not allowed to access this resour…
HTTP 404 Not Found
The server can’t find anything at the requested URL.
HTTP 502 Bad Gateway
A proxy or gateway (Nginx, load balancer, CDN) got an invalid response — or no response — from the upstream server behind it.
java.lang.StringIndexOutOfBoundsException: begin 0, end 10, length 5
substring()/charAt() used an index outside the string.
java.lang.UnsupportedOperationException (List.of / Arrays.asList is immutable)
Code tried to modify an immutable or fixed-size collection.
java.io.IOException: Stream closed
Code read or wrote a stream after it was closed — often by a try-with-resources block or a wrapper closing the underlying stream.
PHP Fatal error: Uncaught Error: Class "X" not found
PHP couldn’t load the class — autoloading failed, the namespace is wrong, or the dependency isn’t installed.
Killed / Out of memory: Killed process (Linux OOM killer)
The kernel ran out of memory and killed a process to recover — the program just prints “Killed” (exit code 137).
Fatal error: Uncaught Error: Call to a member function x() on null
Code called a method on a variable that is null instead of an object.
Fatal error: Uncaught ArgumentCountError: Too few arguments to function foo(), 1 passed and exactly 2 expected
A function was called with fewer arguments than it requires.
Fatal error: Uncaught DivisionByZeroError: Division by zero
Code divided by zero (or used modulo by zero) — PHP 8 throws instead of warning.
Fatal error: Uncaught Exception: message in file.php:12
An exception was thrown and nothing caught it, so PHP stopped the script.
TypeError: can only concatenate str (not "int") to str
You joined a string and a non-string with +.
TypeError: 'str' object is not callable
You used parentheses on something that isn’t a function — often a variable shadowing a built-in.
TypeError: unhashable type: 'list'
A mutable object (list, dict, set) was used as a dict key or set member.
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