[Original] answers to several questions that can definitely test your C language skill

Original post address: http://chimf.bloghome.cn/posts/52793.html

No answers are provided. I wrote a reference answer. I hope you can correct it!

 

Reference answer:

Int x = 35;
Char STR [10];
// Q: What are the values of strlen (STR) and sizeof (STR?
// Reference answer: 13, 10. (In x86 machines -- little endian, descending stack, vc6.0 compiler)
// First, allocate space to X in the stack. Because the stack is little endian and the stack is decreasing, the order of X in the memory is: 00 00 23
// Allocate space to STR in the stack. Because the stack in the vc6.0 compiler is 4-byte aligned by default, 12 bytes of space will be allocated on the stack, and STR points to the lowest address.
// Therefore, in the memory, from low to high: CC 23 00 00 00, strlen (STR) = 13
// P.s. GCC seems that the stack is 16-byte aligned, so the results should be different. This is the case for a company's pen question. I personally feel that this compiler-related result is meaningless.

Strcpy (STR ," Http://www.it315.org "/ * A total of 13 letters */);
// Q: What are the values of x and strlen (STR?
// Reference answer: x = 103, strlen (STR) = 13. Based on the above analysis, this is simple. x = 'G' = 0x67 = 103

STR = "it315.org ";
// Q: Is the compilation successful?
// Reference Answer: No, char STR [10] ;=> char * const STR; pointer constants cannot be assigned again

Char * pstr;
Strcpy (pstr ," Http://www.it315.org/ ");
// Q: Can the above sentence be compiled? Is there a problem when running?
// Reference answer: it can be compiled, but there will be problems during the runtime, because pstr is not allocated memory space

Const char * P1;
Char * const P2;
// Q: What is the difference between the above two statements?
// Reference answer: P1 is a pointer to a constant. That is, P1 ++ is valid. * P1 = 'A' is invalid. P2 pointer is a constant, that is, * P2 = 'A' is legal, P2 ++ is invalid, and P2 must be initialized during definition, such as char * const P2 = STR;

P1 = (const char *) STR;
// Q: If it is p1 = STR; can the compilation be passed? Why type conversion? What is the essence of type conversion?
// Reference Answer: No, because STR is a char * const, and P1 is a const char *
 
Strcpy (P1, "ABC ");
// Q: Can the compilation be passed?
// Reference Answer: No. P1 is a const char * and cannot be changed. The strcpy parameter must be a char *
 
Printf ("% d", STR );

// Q: Is there a problem?
// Reference Answer: No problem. The output result is the value of the STR pointer, that is, an address value (10 hexadecimal)
 
Pstr = 3000;
// Q: Can the compilation be successful? If not, how can I modify it to ensure the compilation is successful?
// Reference Answer: No, pstr = (char *) 3000; you can compile
 
Long y = (long) pstr;
// Q: Can I do this?
// Reference answer: Yes. Y is the value of the pstr pointer, that is, an address.

Int * P = (int *) STR;
* P = 0x00313200;
Printf ("% s", STR );
// Q: What is the result? The following message is displayed: 0x31 corresponds to '1' and 0x32 corresponds to '2 '.
// Reference Answer: No output, STR memory layout: 00 32 31 00...

P = (int *) 3000;
// Q: What is the result of p + 1?
// Reference answer: p + 1 = P + sizeof (INT) = 3004

Char * Pc = new char [100];
// Q: How many memory blocks are occupied by the preceding statement in the memory?
// Reference answer: 104, PC occupies 4 bytes, and 100 bytes are allocated on the stack.

Void test (char ** P)
{
* P = new char [100];
}
// Q: Is there a problem with this compilation function? How do I pass parameters to call this function?
// Reference Answer: No problem, char * pstr; test (& pstr );

// Q: Do you understand the functions of typedef int (* pfun) (int x, int y?
// Reference answer: Define a function pointer type. There are two int parameters and the return value is int.