gmqcc - Man Page

A Quake C compiler built from the NIH realm of sarcastic wit


gmqcc[options] [files...]


Traditionally, a QC compiler reads the file progs.src which in its first line contains the output filename, and the rest is a list of QC source files that are to be compiled in order. gmqcc optionally takes options to specify the output and input files on the commandline, and also accepts assembly files.


gmqcc mostly tries to mimic gcc's commandline handling, though there are also traditional long-options available.

-h, --help

Show a usage message and exit.

-o, --output=filename

Specify the output filename. Defaults to progs.dat. This will overwrite the output file listed in a progs.src file in case such a file is used.


Specify the optimization level


Highest optimization level


Default optimization level


Minimal optimization level


Disable optimization entirely

-Oname, -Ono-name

Enable or disable a specific optimization. Note that these options must be used after setting the optimization level, otherwise they'll be overwritten.


List all possible optimizations and the optimization level they're activated at.

-q, --quiet

Be less verbose. In particular removes the messages about which files are being processed, and which compilation mode is being used, and some others. Warnings and errors will of course still be displayed.

-Dmacroname, -Dmacroname=value

Predefine a macro, optionally with a optional value.


Run only the preprocessor as if -fftepp was used and print the preprocessed code to stdout.

-Wwarning, -Wno-warning

Enable or disable a warning.


Enable almost all warnings. Overrides preceding -W parameters.

The following warnings will not be enabled:

  • -Wuninitialized-global

-Werror, -Wno-error

Controls whether or not all warnings should be treated as errors.

-Werror-warning, -Wno-error-warning

Controls whether a specific warning should be an error.


List all possible warn flags.

-fflag, -fno-flag

Enable or disable a specific compile flag. See the list of flags below.


List all possible compile flags.


Disables colored output


Use an ini file to read all the -O, -W and -f flag from. See the


Turn on some compiler debugging mechanisms.


Turn on compiler mem-check. (Shows allocations and checks for leaks.)


Changes the number of columns to use for the debug memory dump, defaults to 16. Config section about the file format.


Redirects standard output to a file


Redirects standard error to a file


Use the specified standard for parsing QC code. The following standards are available: gmqcc, qcc, fteqcc Selecting a standard also implies some -f options and behaves as if those options have been written right after the -std option, meaning if you changed them before the --std option, you're now overwriting them.

-std=gmqcc includes:

  • -fadjust-vector-fields

  • -fcorrect-logic

  • -ftrue-empty-strings

  • -floop-labels

  • -finitialized-nonconstants

  • -ftranslatable-strings

  • -fno-false-empty-strings

  • -Winvalid-parameter-count

  • -Wmissing-returnvalues

  • -fcorrect-ternary (cannot be turned off)

-std=qcc includes:

  • -fassign-function-types

  • -fIno-adjust-vector-fields

-std=fteqcc includes:

  • -fftepp

  • -ftranslatable-strings

  • -fassign-function-types

  • -Wternary-precedence

  • -fno-adjust-vector-fields

  • -fno-correct-ternary


Adds compiler information to the generated binary file. Currently this includes the following globals:


String containing the compiler version as printed by the --version parameter.

--correct, --no-correct

When enabled, errors about undefined values try to suggest an existing value via spell checking.


DEBUG OPTION. Print the code's intermediate representation before the optimization and finalization passes to stdout before generating the binary.


DEBUG OPTION. Print the code's intermediate representation after the optimization and finalization passes to stdout before generating the binary. The instructions will be enumerated, and values will contain a list of liferanges.

Compile Warnings


Generate a warning about variables which are declared but never used. This can be avoided by adding the ‘noref’ keyword in front of the variable declaration. Additionally a complete section of unreferenced variables can be opened using ‘#pragma noref 1’ and closed via ‘#pragma noref 0’.


Generate a warning if it is possible that a variable can be used without prior initialization. Note that this warning is not necessarily reliable if the initialization happens only under certain conditions. The other way is not possible: that the warning is not generated when uninitialized use is possible.


Generate an error when an unrecognized control sequence in a string is used. Meaning: when there's a character after a backslash in a string which has no known meaning.


Warn when using special extensions which are not part of the selected standard.


Generally QC compilers ignore redeclaration of fields. Here you can optionally enable a warning.


Functions which aren't of type void will warn if it possible to reach the end without returning an actual value.


Warn about a function call with an invalid number of parameters.


Warn when a locally declared variable shadows variable.


Warn when the initialization of a local variable turns the variable into a constant. This is default behaviour unless -finitialized-nonconstants is used.


There are only 2 known global variables of type void: ‘end_sys_globals’ and ‘end_sys_fields’.Any other void-variable will warn.


A global function which is not declared with the ‘var’ keyword is expected to have an implementing body, or be a builtin. If neither is the case, it implicitly becomes a function pointer, and a warning is generated.


Currently there's no way for an in QC implemented function to access variadic parameters. If a function with variadic parameters has an implementing body, a warning will be generated.


Generate warnings about ‘$frame’ commands, for instance about duplicate frame definitions.


Warn about statements which have no effect. Any expression which does not call a function or assigns a variable.


The ‘end_sys_fields’ variable is supposed to be a global variable of type void. It is also recognized as a field but this will generate a warning.


Warn when assigning to a function pointer with an unmatching signature. This usually happens in cases like assigning the null function to an entity's .think function pointer.


Show warnings created using the preprocessor's '#warning' directive.


Warn if there's a preprocessor #if spanning across several files.


Warn about multiple declarations of globals. This seems pretty common in QC code so you probably do not want this unless you want to clean up your code.


The combination of const and var is not illegal, however different compilers may handle them differently. We were told, the intention is to create a function-pointer which is not assignable. This is exactly how we interpret it. However for this interpretation the ‘var’ keyword is considered superfluous (and philosophically wrong), so it is possible to generate a warning about this.


Warn about multibyte character constants, they do not work right now.


Warn if a ternary expression which contains a comma operator is used without enclosing parenthesis, since this is most likely not what you actually want. We recommend the -fcorrect-ternary option.


Warn when encountering an unrecognized ‘#pragma’ line.


Warn about unreachable code. That is: code after a return statement, or code after a call to a function marked as 'noreturn'.


Enable some warnings added in order to help debugging in the compiler. You won't need this.


Warn on an unknown attribute. The warning will inlclude only the first token inside the enclosing attribute-brackets. This may change when the actual attribute syntax is better defined.


Warn when using reserved names such as ‘nil’.


Warn about global constants (using the ‘const’ keyword) with no assigned value.


Warn about global variables with no initializing value. This is off by default, and is added mostly to help find null-values which are supposed to be replaced by the untyped 'nil' constant.


Warn when a variables is redeclared with a different qualifier. For example when redeclaring a variable as ´var´ which was previously marked ´const´.


Similar to the above but for attributes like ‘[[noreturn]]’.


Warn when a function is marked with the attribute "[[deprecated]]". This flag enables a warning on calls to functions marked as such.


Warn about possible mistakes caused by missing or wrong parenthesis, like an assignment in an 'if' condition when there's no additional set of parens around the assignment.


When passing variadic parameters via ...(N) it can happen that incompatible types are passed to functions. This enables several warnings when static typechecking cannot guarantee consistent behavior.


When compiling original id1 QC there is a definition for `break` which conflicts with the 'break' keyword in GMQCC. Enabling this will print a warning when the definition occurs. The definition is ignored for both cases.


When compiling original QuakeWorld QC there are instances where code overwrites constants. This is considered an error, however for QuakeWorld to compile it needs to be treated as a warning instead, as such this warning only works when -std=qcc.


Warn about the use of preprocessor directives inside macros.

Compile Flags


Add some additional characters to the string table in order to compensate for a wrong boundcheck in some specific version of the darkplaces engine.


When assigning to field pointers of type .vector the common behaviour in compilers like fteqcc is to only assign the x-component of the pointer. This means that you can use the vector as such, but you cannot use its y and z components directly. This flag fixes this behaviour. Before using it make sure your code does not depend on the buggy behaviour.


Enable a partially fteqcc-compatible preprocessor. It supports all the features used in the Xonotic codebase. If you need more, write a ticket.


Enable some predefined macros. This only works in combination with ´-fftepp' and is currently not included by '-std=fteqcc'. The following macros will be added:


Note that __FUNC__ is not actually a preprocessor macro, but is recognized by the parser even with the preprocessor disabled.

Note that fteqcc also defines __NULL__ which becomes the first global. Assigning it to a vector does not yield the same result as in gmqcc where __NULL__ is defined to nil (See -funtyped-nil ), which will cause the vector to be zero in all components. With fteqcc only the first component will be 0, while the other two will become the first to of the global return value. This behavior is odd and relying on it should be discouraged, and thus is not supported by gmqcc.


Allow switch cases to use non constant variables.


Perform early out in logical AND and OR expressions. The final result will be either a 0 or a 1, see the next flag for more possibilities.


In many languages, logical expressions perform early out in a special way: If the left operand of an AND yeilds true, or the one of an OR yields false, the complete expression evaluates to the right side. Thus ‘true && 5’ evaluates to 5 rather than 1.


Enable the underscore intrinsic: Using ‘_("A string constant")’ will cause the string immediate to get a name with a "dotranslate_" prefix. The darkplaces engine recognizes these and translates them in a way similar to how gettext works.


Don't implicitly convert initialized variables to constants. With this flag, the const keyword is required to make a constant.


If this flag is not set, (and it is set by default in the qcc and fteqcc standards), assigning function pointers of mismatching signatures will result in an error rather than a warning.


Produce a linenumber file along with the output .dat file.


Use C's operator precedence for ternary expressions. Unless your code depends on fteqcc-compatible behaviour, you'll want to use thi soption.


Normally vectors generate 4 defs, once for the vector, and once for its components with _x, _y, _z suffixes. This option prevents components from being listed.


Most QC compilers translate ‘if(a_vector)’ directly as an IF on the vector, which means only the x-component is checked. This option causes vectors to be cast to actual booleans via a NOT_V and, if necessary, a NOT_F chained to it.

if (a_vector) // becomes
if not(!a_vector)
// likewise
a = a_vector && a_float // becomes
a = !!a_vector && a_float

An empty string is considered to be true everywhere. The NOT_S instruction usually considers an empty string to be false, this option effectively causes the unary not in strings to use NOT_F instead.


An empty string is considered to be false everywhere. This means loops and if statements which depend on a string will perform a NOT_S instruction on the string before using it.


Enable utf8 characters. This allows utf-8 encoded character constants, and escape sequence codepoints in the valid utf-8 range. Effectively enabling escape sequences like '\{x2211}'.


When a warning is treated as an error, and this option is set (which it is by default), it is like any other error and will cause compilation to stop. When disabling this flag by using -fno-bail-on-werror, compilation will continue until the end, but no output is generated. Instead the first such error message's context is shown.


Allow loops to be labeled, and allow 'break' and 'continue' to take an optional label to decide which loop to actually jump out of or continue.

for :outer (i = 0; i < n; ++i) {
    while (inner) {
        if (something)
            continue outer;

Adds a global named 'nil' which is of no type and can be assigned to anything. No typechecking will be performed on assignments. Assigning to it is forbidden, using it in any other kind of expression is also not allowed.

Note that this is different from fteqcc's __NULL__: In fteqcc, __NULL__ maps to the integer written as '0i'. It's can be assigned to function pointers and integers, but it'll error about invalid instructions when assigning it to floats without enabling the FTE instruction set. There's also a bug which allows it to be assigned to vectors, for which the source will be the global at offset 0, meaning the vector's y and z components will contain the OFS_RETURN x and y components.

In that gmqcc the nil global is an actual global filled with zeroes, and can be assigned to anything including fields, vectors or function pointers, and they end up becoming zeroed.


Various effects, usually to weaken some conditions.

with -funtyped-nil

Allow local variables named ‘nil’.(This will not allow declaring a global of that name.)


Allow variadic parameters to be accessed by QC code. This can be achieved via the '...' function, which takes a parameter index and a typename.


void vafunc(string...count) {
    float i;
    for (i = 0; i < count; ++i)
        print(...(i, string), "\n");

Most Quake VMs, including the one from FTEQW or up till recently Darkplaces, do not cope well with vector instructions with overlapping input and output. This option will avoid producing such code.


Usually builtin-numbers are just immediate constants. With this flag expressions can be used, as long as they are compile-time constant.


void printA() = #1; // the usual way
void printB() = #2-1; // with a constant expression

Enabiling this option will allow assigning values or expressions to the return keyword as if it were a local variable of the same type as the function's signature's return type.


float bar() { return 1024; }
float fun() {
    return = bar();
    return; // returns value of bar

When passing on varargs to a different functions, this turns some static error cases into warnings. Like when the caller's varargs are restricted to a different type than the callee's parameter. Or a list of unrestricted varargs is passed into restricted varargs.


Always use STORE_F, LOAD_F, STOREP_F when accessing scalar variables. This is somewhat incorrect assembly instruction use, but in all engines they do exactly the same. This makes disassembly output harder to read, breaks decompilers, but causes the output file to be better compressible.


In commutative instructions, always put the lower-numbered operand first. This shaves off 1 byte of entropy from all these instructions, reducing compressed size of the output file.



Some general peephole optimizations. For instance the code `a = b + c` typically generates 2 instructions, an ADD and a STORE. This optimization removes the STORE and lets the ADD write directly into A.


Tail recursive function calls will be turned into loops to avoid the overhead of the CALL and RETURN instructions.


Make all functions which use neither local arrays nor have locals which are seen as possibly uninitialized use the same local section. This should be pretty safe compared to other compilers which do not check for uninitialized values properly. The problem is that there's QC code out there which really doesn't initialize some values. This is fine as long as this kind of optimization isn't used, but also, only as long as the functions cannot be called in a recursive manner. Since it's hard to know whether or not an array is actually fully initialized, especially when initializing it via a loop, we assume functions with arrays to be too dangerous for this optimization.


This promotes locally declared variables to "temps". Meaning when a temporary result of an operation has to be stored somewhere, a local variable which is not 'alive' at that point can be used to keep the result. This can reduce the size of the global section. This will not have declared variables overlap, even if it was possible.


Causes temporary values which do not need to be backed up on a CALL to not be stored in the function's locals-area. With this, a CALL to a function may need to back up fewer values and thus execute faster.


Don't generate defs for immediate values or even declared constants. Meaning variables which are implicitly constant or qualified as such using the 'const' keyword.


Aggressively reuse strings in the string section. When a string should be added which is the trailing substring of an already existing string, the existing string's tail will be returned instead of the new string being added.

For example the following code will only generate 1 string:

print("Hello you!\n");
print("you!\n"); // trailing substring of "Hello you!\n"

There's however one limitation. Strings are still processed in order, so if the above print statements were reversed, this optimization would not happen.


By default, all parameters of a CALL are copied into the parameter-globals right before the CALL instructions. This is the easiest and safest way to translate calls, but also adds a lot of unnecessary copying and unnecessary temporary values. This optimization makes operations which are used as a parameter evaluate directly into the parameter-global if that is possible, which is when there's no other CALL instruction in between.


Usually an empty RETURN instruction is added to the end of a void typed function. However, additionally after every function a DONE instruction is added for several reasons. (For example the qcvm's disassemble switch uses it to know when the function ends.). This optimization replaces that last RETURN with DONE rather than adding the DONE additionally.


Because traditional QC code doesn't allow you to access individual vector components of a computed vector without storing it in a local first, sometimes people multiply it by a constant like ‘'0 1 0'’ to get, in this case, the y component of a vector. This optimization will turn such a multiplication into a direct component access. If the factor is anything other than 1, a float-multiplication will be added, which is still faster than a vector multiplication.


For constant expressions that result in dead code (such as a branch whos condition can be evaluated at compile-time), this will eliminate the branch and else body (if present) to produce more optimal code.


The configuration file is similar to regular .ini files. Comments start with hashtags or semicolons, sections are written in square brackets and in each section there can be arbitrary many key-value pairs.

There are 3 sections currently: ‘flags’,‘warnings’,‘optimizations’.They contain a list of boolean values of the form ‘VARNAME = true’ or ‘VARNAME = false’.The variable names are the same as for the corresponding -W, -f or -O flag written with only capital letters and dashes replaced by underscores.

Here's an example:

# a GMQCC configuration file
    FTEPP = true
    LNO = true


    PEEPHOLE = true



A documented example for a gmqcc.ini file.

See Also



See <>.


Currently the '-fftepp-predefs' flag is not included by '-std=fteqcc', partially because it is not entirely conformant to fteqcc.

Please report bugs on <>, or see <> on how to contact us.

Referenced By


January 24, 2013