C programming FAQ Summary

1. forget the annotation Terminator code a = B;/* The bugc = d appears;/* c = d will not be executed */2. unexpected value assignment/unexpected bool Expression Code: if (a = B) c;/* a is always equal to B, only when B! If (0 <a <5) c;/* Boolean expression is always true */the bool expression in the above Code is always true, since the value of 0 <a is 0 or 1, it is always less than 5. Of course, there is no bool expression in C. Here we only assume 3. defective macro code: # define assign (a, B) a = (char) bassign (x, y> 8) to x = (char) y> 8/* may not be your goal */4. unmatched header file code: // foo. h: struct foo {BOOL a}; // F1.c # define BOOL char # include "foo. h "// F2.c # define BOOL int # include" foo. h "F1 and F2 have different definitions of the BOOL type in the structure foo. If the interaction occurs, error 5 is displayed. you may write the following code for erratic return values: int foo (a) {if (a) return (1) ;}/* Bug, because sometimes no value is returned */6. for an unpredictable struct, see the following bit Package Structure: struct eeh_type {uint16 size: 10;/* 10 bits */uint16 code: 6;/* 6 bits */}; depending on which C compiler is used and the size of your machine is used, this code is implemented as follows: <10-bits> <6-bits> or <6-bits> <10-bits> depends on the C compiler, machine architecture, and incredible priority settings, these items may be aligned to the nearest 8, 16, 32, or 64 bits. 7. uncertain order of evaluation foo (pointer-> member, pointer = & buffer [0]); different compilers have different order of evaluation for function parameters, gcc is the order of evaluation from left to right, and some compilers are 8 from right to left. code of block scope that is easy to change: if (...) foo (); else bar (); Debugging output: if (...) foo (); else printf ("Calling bar ()");/* Note! Else stops here */bar ();/* Note! Bar will always be executed */9. unsafe return value code: char * f () {char result [80]; sprintf (result, "anything will do"); return (result);/* Note! Result is allocated to the stack. */} int g () {char * p; p = f (); printf ("f () returns: % s \ n", p);} 10. side effects is not defined. Even if a simple expression is used, C does not define the order of side effects. The result depends on your compiler. I/I ++ may be equal to 0 or 1, see the following code: # include <stdio. h> int foo (int n) {printf ("Foo got % d \ n", n); return (0);} int bar (int n) {printf ("Bar got % d \ n", n); return (0);} int main (int argc, char * argv []) {int m = 0; int (* (fun_array [3]) (); int I = 1; int ii = I/++ I; printf ("I/++ I = % D, ", ii); fun_array [1] = foo; fun_array [2] = bar; (fun_array [++ m]) (++ m); return 0 ;} 11. uninitialized local variables are not so well-known in fact, but they won't be lost to other bugs in the event of severity. See the following code: void foo (a) {int B; if (B) {/* bug! B is not initialized */} modern compiler will issue an error warning, read the following code: void foo (int a) {BYTE * B; if () B = Malloc (a); if (B) {/* BUG! B may not be initialized */* B = a;} 12. During the messy compilation environment, the environment generates hundreds of thousands of compilation information. We do not know much about this. Some dangerous common names are difficult to find: # include <stdio. h> # define BUFFSIZE 2048 long foo [BUFSIZ]; // note the spelling: BUFSIZ! = The BUFFSIZE compiler will not report an error because the BUFSIZ is already in stdio. h defines 13. in C, the number of BITs starts from 0. If no '8' or '9' appears in the number, the compiler will not warn int numbers [] = {001,010, // 8 instead of 10 014}; // 12 instead of 14. there may be various errors in the signed char in the signed character C. For example, 128 is a negative number. In addition, you must be very careful when using low-precision integers, C makes it easy to ignore char s = 127; unsigned char u = 127; s ++;/* the result is a negative number */if (s <u) {/* true! */} If (s> 127) {/* may never be true */} if (u <0) {/* may never be true */} 15. bad "standard library" code: {int a = 1, B = 2; char buf [10]; scanf ("% d", a, B ); // & a, & B? Sprintf (buf, "this is the result: % d"); // overflow}