These fuctions do not need to include any header file to use them. So it provides faster usage, as these are Built-in functions of GCC compiler which is most used compiler, even in competitive programming.

Note: If the compiler shows warning of overflow, use casting before __builtin_inf() function as

(data_type)__builtin_inf()

1. __builtin_inf(void): This function returns positive infinity which will then converted to DBL_MAX of C language limits.h header file Macro. Its return data type is double.
   Example:

   if __builtin_inf() is used
   it returns infinte
   
   Output: inf
   

   Here is a C++ program which shows the use of this function:

   
   
   
   
   
   

   
   
   

   #include <iostream> using namespace std;    int main() {     // infinite value (<b>inf</b>)     double double_inf = __builtin_inf();        cout << double_inf << endl;     return 0; }
   Output:

   inf
   

2. __builtin_infd32(void): These function returns maximum value of 4-byte integer and return data type is 32-bit integer.

   Example:

   if __builtin_infd32() is used
   it returns the maximum value of
   the 32-bit integer
   
   Output: 2147483647
   

   Here is a C++ program which shows the use of this function:

   
   

   
   
   

   #include <iostream> using namespace std;    int main() {     // function returns highest signed integer value     int int_inf = (int)__builtin_infd32();        // you can use __builtin_inf() function     // as well and then cast to integer     int int_inf2 = (int)__builtin_inf();        cout << int_inf << endl;     cout << int_inf2 << endl;        // function returns highest unsigned integer value     unsigned int unsinged_int_inf         = (unsigned int)__builtin_infd32();        // you can use __builtin_inf() function as well     // and then cast to unsigned integer     unsigned int unsinged_int_inf2         = (unsigned int)__builtin_inf();        cout << unsinged_int_inf << endl;     cout << unsinged_int_inf2 << endl;        return 0; }
   Output:

   2147483647
   2147483647
   4294967295
   4294967295
   

3. __builtin_infd64(void): This function returns Highest value that can be represented by 8 byte integer which is highest value of integer we can use in C++.

   Example:

   if __builtin_infd64() is used
   it returns the maximum value of
   the 64-bit integer
   
   Output: 9223372036854775807
   

   Here is a C++ program which shows the use of this function:

   
   

   
   
   

   #include <iostream> using namespace std;    int main() {     // highest signed 8 byte value     long long int long_inf = (long long int)__builtin_infd64();        // you can use __builtin_inf() as well     // and then cast to long long int     long long int long_inf2         = (long long int)__builtin_inf();        cout << long_inf << endl;     cout << long_inf2 << endl;        // highest unsiged 8 byte value     unsigned long long int unsigned_longlong_inf         = (unsigned long long int)__builtin_infd64();        // you can use __builtin_inf() as well     // and then cast to unsigned long long int     unsigned long long int unsigned_longlong_inf2         = (unsigned long long int)__builtin_inf();        cout << unsigned_longlong_inf << endl;     cout << unsigned_longlong_inf2 << endl;     return 0; }
   Output:

   9223372036854775807
   9223372036854775807
   18446744073709551615
   18446744073709551615
   

4. __builtin_infd128(void): As the maximum size that can be used for integer is 64-bit in C/C++, this function give the same result as __builtin_infd64().

   Example:

   
   
   
   

   if __builtin_infd128() is used
   it returns the maximum value of
   the 64-bit integer
   
   Output: 9223372036854775807
   

5. __builtin_inff(void): These function returns float maximum value means 4-byte maximum decimal point value.

   Example:

   if __builtin_inff() is used
   it returns the maximum value of
   the 32-bit float
   
   Output: inf
   

   Here is a C++ program which shows the use of this function:

   
   

   
   
   

   #include <iostream> using namespace std;    int main() {     float float_inf = __builtin_inff();        // you can use __builtin_inf() as well     // and then cast it to float data type     float float_inf2 = (float)__builtin_inf();        cout << float_inf << endl;     cout << float_inf2 << endl;     return 0; }
   Output:

   inf
   inf
   

6. __builtin_infl(void): These function returns maximum long double data type value.

   Example:

   if __builtin_infl() is used
   it returns the maximum value of
   the long double type
   
   Output: inf
   

   Here is a C++ program which shows the use of this function:

   
   

   
   
   

   #include <iostream> using namespace std;    int main() {     long double long_double_inf = __builtin_infl();        // you can use __builtin_inf() as well     // and then cast it to float data type     long double long_double_inf2         = (long double)__builtin_inf();        cout << long_double_inf << endl;     cout << long_double_inf2 << endl;     return 0; }
   Output:

   inf
   inf
   

7. In the recent versions of GCC compiler, these are two new functions: __builtin_infn(void) & __builtin_infnx(void). One can replace n with 32 or 64 and it will return inf value respectively of 32-bit, 64-bit.

Similar article: Builtin functions of GCC compiler