Error map
not a member of std C++: error: 'optional' in namespace 'std' does not name a template type — wrong -std standard
C/C++ · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (7). 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 (7)
C++: error: 'x' was not declared in this scope (undeclared identifier)
The compiler met a name it has never seen: it is misspelled, declared later, out of scope, or its header or namespace is missing.
C/C++: fatal error: foo.h: No such file or directory — #include not found
The preprocessor cannot find a header named in `#include`: wrong path, missing include directory (-I), or the library is not inst…
C++: error: redefinition of 'class X' / multiple definition — missing include guard
The same class, struct or function body was included twice in one translation unit because the header has no include guard.
C++: error: 'string' does not name a type
Where the compiler expected a type, it found a name it does not know as one — a missing header, namespace, or class declared late…
Make: *** No rule to make target 'foo.c', needed by 'foo.o'. Stop.
`make` was asked to build a file for which there is no rule and no existing file — a missing source, a typo in the Makefile, or a…
Make: Makefile:5: *** missing separator. Stop. (spaces instead of a tab)
A line in the Makefile is neither a rule, a variable assignment nor a tab-indented command — nearly always spaces used where a TA…
CMake Error: Could not find a package configuration file provided by "Foo" (requested version 1.2)
`find_package(Foo)` could not locate the library's CMake config (FooConfig.cmake or FindFoo.cmake), so the library is not install…
Two steps away (11)
C/C++: undefined reference to `function' — collect2: error: ld returned 1 exit status
The linker can’t find the definition of a function or variable that was declared and used.
C/C++: error: expected ';' before 'x' — missing semicolon
The compiler reached a token where a statement should have ended — almost always a missing semicolon on the line above.
C++: error: expected primary-expression before ')' token
The parser expected a value or expression and found a token that cannot start one — often a type name passed where a value belong…
bash: command not found
The shell can’t find an executable with that name in any directory on your PATH.
C/C++: undefined reference to `main' — (.text+0x20) in crt1.o
The linker has no `main` function: the file with `main` is not compiled or linked, or `main` is spelled or declared incorrectly.
C++: error: invalid use of incomplete type 'class X' — forward declaration only
You used a class that has only been forward-declared (so its size and members are unknown) where the full definition is required.
C: warning: implicit declaration of function 'foo' [-Wimplicit-function-declaration]
In C you called a function the compiler has not seen declared — usually a missing `#include`. Newer compilers treat it as an erro…
C/C++: multiple definition of `x'; first defined here — ld returned 1 exit status
The linker found the same function or global variable defined in two object files — usually something defined in a header.
Go: declared and not used: x / "fmt" imported and not used
Go refuses to compile code with unused local variables or unused imports.
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…
C++: error: invalid conversion from 'const char*' to 'char*' [-fpermissive]
C++ forbids silently dropping `const` or converting between unrelated pointer types — typically a string literal assigned to `cha…
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