Computer Science

Semantic Analysis Checks using Coded Examples

vkungeLeave a comment

Checks in semantic analysis include:

  • Type checking :
    • Type mismatch checking. E.g,
  int x = “Hello”;  
  • Type cast checking. E.g,
int radius = 3;
float Pi = 3.14;
float diameter = 2*radius*Pi; 
/*radius will be typecast to float
during the calculation, i.e 3.00 
(This result is reflected in the next step, 
intermediate code generation
 as  TAC)
*/


the TAC code generated from the above example:

t1 = 2.0  // Represents the float constant 2.0
t2 = (float)radius  // Type casting 'radius' to float
t3 = t1 * t2  // Multiplying 2.0 by the type-casted 'radius'
t4 = t3 * Pi  // Multiplying the result by 'Pi'
  • Variable Declaration checks :

    • Ensuring all variables are declared. Eg,
int x = 10;
int y = 10;
sum = x+y; //sum was not declared
  • Reserved identifier / keyword use. E.g,
int char = '1';//char is a reserved identifier
int char_2;

int if; //if is a reserved keyword
int if_2;
  • Variable scope check

    A unique variable declared within a function cannot be used by any other structures or functions outside of the original function block. Eg,
void demoFunction() 
{
    int uniqueX = 10;
}

int main() 
{
    printf("%d\n", uniqueX); // Error: 'uniqueX' is out of scope
    return 0;
}
  • Function Declaration and Invocation checks:
    • Function declaration check – missed function declaration. e.g
int main() {
    // Calling a function before it is declared or defined
    hello(); // Error: 'hello' is called before declaration/definition
    
    return 0;
}
/*the declaration was omitted, 
this function declaration
is required: 

void hello();

*/
void hello() {
    // Function definition for 'hello'
    printf("Hello, world!\n");
}
  •  Function declaration check – missing function implementation when a function prototype (function declaration) was declared. E.g,
// Function prototype (declaration)
int multiply(int a, int b);

int main() {
    int result = multiply(3, 7); /* Error: Function 
                                'multiply' 
                                is declared but not 
                                defined/implemented*/    
    return 0;
}
  • Function invocation checks.

(NB, function invocation simply means to call a function correctly)

int add(int a, int b);

int add(int a, int b) {
    return a + b;
}

int main() {
    int sum1 = add(5, 10, 15); /* Error: Too many arguments
                                in the function call*/
                                
    int sum2 = add(5);/*Error: Missing arguments 
                        in the function call*/
                        
    int sum3 = add(1,2) /*proper invocation of add,
                        no error here*/
    return 0;
}
  • Control Flow Checks -Verify the correct structure and use of control structures: if, while, for etc

Other checks exist , we have only examined some of the main semantic checks.

Recall that once all semantic checks are passed, Intermediate code generation occurs next.

Examples of Semantic errors in C

ExampleDescription/Explanation
int a = “hello”;Type mismatch: assigning a string to an integer variable.
int a; return a;Using uninitialized variable a.
int a = 5 / 0;Division by zero.
char *str = malloc(10); free(str); str[0] = ‘A’;Using a pointer str after it has been freed.
int* ptr; *ptr = 10;Dereferencing an uninitialized pointer ptr.
int arr[5]; arr[10] = 50;Array index out of bounds.
double result = sqrt(-1);Passing invalid argument to a function (e.g., square root of a negative number).
FILE *fp = fopen(“nonexistent.txt”, “r”); if(fp) { /* … */ }Incorrect error checking on fopen. Should be if(!fp) for error checking.

© 2024  Vedesh Kungebeharry. All rights reserved. 

Leave a comment