How are macros undefined in C?
Macros can be undefined from the command line using the /U option, followed by the macro names to be undefined. The effect of issuing this command is equivalent to a sequence of #undef macro-name statements at the beginning of the file.
What is the use of #undef in C?
Description. In the C Programming Language, the #undef directive tells the preprocessor to remove all definitions for the specified macro. A macro can be redefined after it has been removed by the #undef directive. Once a macro is undefined, an #ifdef directive on that macro will evaluate to false.
What is #if defined in C?
In the C Programming Language, the #ifdef directive allows for conditional compilation. The preprocessor determines if the provided macro exists before including the subsequent code in the compilation process.
Can you redefine a macro in C?
Once you’ve defined a macro, you can’t redefine it to a different value without first removing the original definition. However, you can redefine the macro with exactly the same definition. Thus, the same definition may appear more than once in a program. The #undef directive removes the definition of a macro.
What is #line in C?
#line directive (C/C++)
The #line directive tells the preprocessor to set the compiler’s reported values for the line number and filename to a given line number and filename.
What are macros in C?
Overview. Macro in C programming is known as the piece of code defined with the help of the #define directive. Macros in C are very useful at multiple places to replace the piece of code with a single value of the macro. Macros have multiple types and there are some predefined macros as well.
Can we use Elif in C?
In the C Programming Language, the #elif provides an alternate action when used with the #if, #ifdef, or #ifndef directives.
What is a macro definition in C?
In C, A macro is any constant value or variable with its value. And the macro name will get replaced by its value in the entire program. Macros help in writing less code and also in saving time.
Why we use #define in C?
Remarks. The #define directive causes the compiler to substitute token-string for each occurrence of identifier in the source file. The identifier is replaced only when it forms a token. That is, identifier is not replaced if it appears in a comment, in a string, or as part of a longer identifier.
How will you override an existing macro in C?
Answer: To override an existing macro, we need to undefine existing macro using “#undef”. Then, we need to define same macro again with new value.
Why pragma is used in C?
The ‘ #pragma ‘ directive is the method specified by the C standard for providing additional information to the compiler, beyond what is conveyed in the language itself. The forms of this directive (commonly known as pragmas) specified by C standard are prefixed with STDC .
Why we use conio h in C language?
h is a C header file used mostly by MS-DOS compilers to provide console input/output. It is not part of the C standard library or ISO C, nor is it defined by POSIX. This header declares several useful library functions for performing “istream input and output” from a program.
How many macros are there in C?
There are two types of macros: Object-like Macros. Function-like Macros.
What are the types of macros?
Types of macros
- Executive macros.
- Declarative macros.
What does #elif mean in C?
“else if
‘ #elif ‘ stands for “else if”. Like ‘ #else ‘, it goes in the middle of a conditional group and subdivides it; it does not require a matching ‘ #endif ‘ of its own. Like ‘ #if ‘, the ‘ #elif ‘ directive includes an expression to be tested.
Can we use #if in C?
Yes, both C and C++ allow us to nested if statements within if statements, i.e, we can place an if statement inside another if statement.
Why macros are used in C?
In C, the macro is used to define any constant value or any variable with its value in the entire program that will be replaced by this macro name, where macro contains the set of code that will be called when the macro name is used in the program.
What is the syntax of #define in C?
The syntax for creating a constant using #define in the C language is: #define CNAME value. OR #define CNAME (expression) CNAME. The name of the constant. Most C programmers define their constant names in uppercase, but it is not a requirement of the C Language.
What type is #define in C?
#define in C is a directive which is used to #define alias. Difference between typedef and #define: typedef is limited to giving symbolic names to types only, whereas #define can be used to define an alias for values as well, e.g., you can define 1 as ONE, 3.14 as PI, etc.
How do I redefine a macro?
The process to redefine a Macro is:
Macro must be defined. When, you want to redefine the Macro, first of all, undefined the Macro by using #undef preprocessor directive. And, then define the Macro again by using #define preprocessor directive.
How do you change #define value in C?
You can’t change it at run time, if that’s what you mean. However, one of the purposes of #define’s in C code is to select options that will be used with #ifdef or #ifndef to determine whether particular pieces of code are present. You can change the value specified for any given #define and recompile.
What is __ attribute __ in C?
The __attribute__ directive is used to decorate a code declaration in C, C++ and Objective-C programming languages. This gives the declared code additional attributes that would help the compiler incorporate optimizations or elicit useful warnings to the consumer of that code.
What is GCC pragma?
GCC supports several types of pragmas, primarily in order to compile code originally written for other compilers. Note that in general we do not recommend the use of pragmas; See Function Attributes, for further explanation.
Where is Clrscr used?
Clrscr() Function in C
h” (console input output header file) used to clear the console screen. It is a predefined function, by using this function we can clear the data from console (Monitor). Using of clrscr() function in C is always optional but it should be place after variable or function declaration only.
What is the purpose of Clrscr () printf () and getch ()?
clrscr() – This function is used to clear the previous output from the console. printf() – The printf() function is used to print data which is specified in the brackets on the console. getch() – This function requests for a single character. Until you press any key it blocks the screen.