You can integrate YARA into your C/C++ project by using the API privided by the libyara library. This API gives you access to every YARA feature and it’s the same API used by the command-line tools yara and yarac.

Initalizing and finalizing libyara

The first thing your program must do when using libyara is initializing the library. This is done by calling the yr_initialize() function. This function allocates any resources needed by the library and initalizes internal data structures. Its counterpart is yr_finalize(), which must be called when you are finished using the library.

In a multi-threaded program only the main thread must call yr_initialize() and yr_finalize(), but any additional thread using the library must call yr_finalize_thread() before exiting.

Compiling rules

Before using your rules to scan any data you need to compile them into binary form. For that purpose you’ll need a YARA compiler, which can be created with yr_compiler_create(). After being used, the compiler must be destroyed with yr_compiler_destroy().

You can use either yr_compiler_add_file() or yr_compiler_add_string() to add one or more input sources to be compiled. Both of these functions receive an optional namespace. Rules added under the same namespace behaves as if they were contained within the same source file or string, so, rule identifiers must be unique among all the sources sharing a namespace. If the namespace argument is NULL the rules are put in the default namespace.

Both yr_compiler_add_file() and yr_compiler_add_string() return the number of errors found in the source code. If the rules are correct they will return 0. For more detailed error information you must set a callback function by using yr_compiler_set_callback() before calling yr_compiler_add_file() or yr_compiler_add_string(). The callback function has the following prototype:

void callback_function(
    int error_level,
    const char* file_name,
    int line_number,
    const char* message)

Possible values for error_level are YARA_ERROR_LEVEL_ERROR and YARA_ERROR_LEVEL_WARNING. The arguments file_name and line_number contains the file name and line number where the error or warning occurs. file_name is the one passed to yr_compiler_add_file(). It can be NULL if you passed NULL or if you’re using yr_compiler_add_string().

After you successfully added some sources you can get the compiled rules using the yr_compiler_get_rules() function. You’ll get a pointer to a YR_RULES structure which can be used to scan your data as described in Scanning data. Once yr_compiler_get_rules() is invoked you can not add more sources to the compiler, but you can get multiple instances of the compiled rules by calling yr_compiler_get_rules() multiple times.

Each instance of YR_RULES must be destroyed with yr_rules_destroy().

Saving and retrieving compiled rules

Compiled rules can be saved to a file and retrieved later by using yr_rules_save() and yr_rules_load(). Rules compiled and saved in one machine can be loaded in another machine as long as they have the same endianness, no matter the operating system or if they are 32-bits or 64-bits systems. However files saved with older versions of YARA may not work with newer version due to changes in the file layout.

Scanning data

Once you have an instance of YR_RULES you can use it to scan data either from a file or a memory buffer with yr_rules_scan_file() and yr_rules_scan_mem() respectively. The results from the scan are notified to your program via a callback function. The callback has the following prototype:

int callback_function(
    int message,
    void* message_data,
    void* user_data);

Possible values for message are:


Your callback function will be called once for each existing rule with either a CALLBACK_MSG_RULE_MATCHING or CALLBACK_MSG_RULE_NOT_MATCHING message, depending if the rule is matching or not. In both cases a pointer to the YR_RULE structure associated to the rule is passed in the message_data argument. You just need to perform a typecast from void* to YR_RULE* to access the structure.

The callback is also called once for each imported module, with the CALLBACK_MSG_IMPORT_MODULE message. In this case message_data points to a YR_MODULE_IMPORT structure. This structure contains a module_name field pointing to a null terminated string with the name of the module being imported and two other fields module_data and module_data_size. These fields are initially set to NULL and 0 , but your program can assign a pointer to some arbitrary data to module_data while setting module_data_size to the size of the data. This way you can pass additional data to those modules requiring it, like the Cuckoo module for example.

Lastly, the callback function is also called with the CALLBACK_MSG_SCAN_FINISHED message when the scan is finished. In this case message_data is NULL.

In all cases the user_data argument is the same passed to yr_rules_scan_file() or yr_rules_scan_mem(). This pointer is not touched by YARA, it’s just a way for your program to pass arbitrary data to the callback function.

Both yr_rules_scan_file() and yr_rules_scan_mem() receive a flags argument and a timeout argument. The only flag defined at this time is SCAN_FLAGS_FAST_MODE, so you must pass either this flag or a zero value. The timeout argument forces the function to return after the specified number of seconds aproximately, with a zero meaning no timeout at all.

The SCAN_FLAGS_FAST_MODE flag makes the scanning a little faster by avoiding multiple matches of the same string when not necessary. Once the string was found in the file it’s subsequently ignored, implying that you’ll have a single match for the string, even if it appears multiple times in the scanned data. This flag has the same effect of the -f command-line option described in Running YARA from the command-line.

API reference

Data structures


Data structure representing a YARA compiler.


Data structure representing a set of compiled rules.


Data structure representing a single rule.

const char* identifier

Rule identifier.

const char* tags

Pointer to a sequence of null terminated strings with tag names. An additional null character marks the end of the sequence. Example: tag1\0tag2\0tag3\0\0. To iterate over the tags you can use yr_rule_tags_foreach().

YR_META* metas

Pointer to a sequence of YR_META structures. To iterate over the structures use yr_rule_metas_foreach().

YR_STRING* strings

Pointer to a sequence of YR_STRING structures. To iterate over the structures use yr_rule_strings_foreach().


Data structure representing a metadata value.

const char* identifier

Meta identifier.

int32_t type

One of the following metadata types:


Data structure representing a string declared in a rule.

const char* identifier

String identifier.


Data structure representing a string match.

int64_t base

Base offset/address for the match. While scanning a file this field is usually zero, while scanning a process memory space this field is the virtual address of the memory block where the match was found.

int64_t offset

Offset of the match relative to base.

int32_t length

Length of the matching string

uint8_t* data

Pointer to the matching string.

const char* module_name

Name of the module being imported.

void* module_data

Pointer to additional data passed to the module. Initially set to NULL, your program is responsible of setting this pointer while handling the CALLBACK_MSG_IMPORT_MODULE message.

size_t module_data_size

Size of additional data passed to module. Your program must set the appropriate value if module_data is modified.


void yr_initialize(void)

Initalize the library. Must be called by the main thread before using any other function.

void yr_finalize(void)

Finalize the library. Must be called by the main free to release any resource allocated by the library.

void yr_finalize_thread(void)

Any thread using the library, except the main thread, must call this function when it finishes using the library.

int yr_compiler_create(YR_COMPILER** compiler)

Create a YARA compiler. You must pass the address of a pointer to a YR_COMPILER, the function will set the pointer to the newly allocated compiler. Returns one of the following error codes:

void yr_compiler_destroy(YR_COMPILER* compiler)

Destroy a YARA compiler.

void yr_compiler_set_callback(YR_COMPILER* compiler, YR_COMPILER_CALLBACK_FUNC callback)

Set a callback for receiving error and warning information.

int yr_compiler_add_file(YR_COMPILER* compiler, FILE* file, const char* namespace, const char* file_name)

Compile rules from a file. Rules are put into the specified namespace, if namespace is NULL they will be put into the default namespace. file_name is the name of the file for error reporting purposes and can be set to NULL. Returns the number of errors found during compilation.

int yr_compiler_add_string(YR_COMPILER* compiler, const char* string, const char* namespace_)

Compile rules from a string. Rules are put into the specified namespace, if namespace is NULL they will be put into the default namespace. Returns the number of errors found during compilation.

int yr_compiler_get_rules(YR_COMPILER* compiler, YR_RULES** rules)

Get the compiled rules from the compiler. Returns one of the following error codes:

void yr_rules_destroy(YR_RULES* rules)

Destroy compiled rules.

int yr_rules_save(YR_RULES* rules, const char* filename)

Save rules into the file specified by filename. Returns one of the following error codes:

int yr_rules_load(const char* filename, YR_RULES** rules)

Load rules from the file specified by filename. Returns one of the following error codes:

int yr_rules_scan_mem(YR_RULES* rules, uint8_t* buffer, size_t buffer_size, int flags, YR_CALLBACK_FUNC callback, void* user_data, int timeout)

Scan a memory buffer. Returns one of the following error codes:

int yr_rules_scan_file(YR_RULES* rules, const char* filename, int flags, YR_CALLBACK_FUNC callback, void* user_data, int timeout)

Scan a file. Returns one of the following error codes:

yr_rule_tags_foreach(rule, tag)

Iterate over the tags of a given rule running the block of code that follows each time with a different value for tag of type const char*. Example:

const char* tag;

/* rule is a YR_RULE object */

yr_rule_tags_foreach(rule, tag)
{ something with tag
yr_rule_metas_foreach(rule, meta)

Iterate over the YR_META structures associated to a given rule running the block of code that follows each time with a different value for meta. Example:

YR_META* meta;

/* rule is a YR_RULE object */

yr_rule_metas_foreach(rule, meta)
{ something with meta
yr_rule_strings_foreach(rule, string)

Iterate over the YR_STRING structures associated to a given rule running the block of code that follows each time with a different value for string. Example:

YR_STRING* string;

/* rule is a YR_RULE object */

yr_rule_strings_foreach(rule, string)
{ something with string
yr_string_matches_foreach(string, match)


YR_MATCH* match;

/* string is a YR_STRING object */

yr_string_matches_foreach(string, match)
{ something with match

Error codes


Everything went fine.


Insuficient memory to complete the operation.


File could not be opened.


File could not be mapped into memory.


File length is zero.


File is not a valid rules file.


Rules file is corrupt.


File was generated by a different YARA and can’t be loaded by this version.


Too many threads trying to use the same YR_RULES object simultaneosly. The limit is defined by MAX_THREADS in ./include/yara/limits.h


Scan timed out.


Callback returned an error.


Too many matches for some string in your rules. This usually happens when your rules contains very short or very common strings like 01 02 or FF FF FF FF. The limit is defined by MAX_STRING_MATCHES in ./include/yara/limits.h