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Is exit status truly equivalent to returning the same status from main?
Is exit status truly equivalent to returning the same status from main? Yes and no. The Standard says that a return from the initial call to main is equivalent to calling exit. However, a return from main cannot be expected to work if data local to main might be needed during cleanup;A few very old,... 2015-12-16, 1376👍, 0💬

How can I write a generic macro to swap two values?
How can I write a generic macro to swap two values? There is no good answer to this question. If the values are integers, a well-known trick using exclusive-OR could perhaps be used, but it will not work for floating-point values or pointers, or if the two values are the same variable. If the macro ... 2016-02-24, 1375👍, 0💬

Can I use base-2 constants (something like 0b101010)? Is there a printf format for binary?
Can I use base-2 constants (something like 0b101010)? Is there a printf format for binary? No, on both counts, although there are various preprocessor tricks you can try. You can convert base-2 string representations to integers with strtol. If you need to print numbers out in base 2, . 2015-02-13, 1375👍, 0💬

What should malloc0 do? Return a null pointer or a pointer to 0 bytes?
What should malloc0 do? Return a null pointer or a pointer to 0 bytes? The ANSI/ISO Standard says that it may do either; the behavior is implementation-defined Portable code must either take care not to call malloc(0), or be prepared for the possibility of a null return. 2015-12-04, 1374👍, 0💬

What is assert and when would I use it?
What is assert and when would I use it? It is a macro, defined in &lt;assert.h>, for testing ``assertions''. An assertion essentially documents an assumption being made by the programmer, an assumption which, if violated, would indicate a serious programming error. For example, a function which ... 2015-01-12, 1371👍, 0💬

What is the difference between memcpy and memmove?
What is the difference between memcpy and memmove? memmove offers guaranteed behavior if the memory regions pointed to by the source and destination arguments overlap. memcpy makes no such guarantee, and may therefore be more efficiently implementable. When in doubt, it's safer to use memmove. It se... 2015-12-07, 1370👍, 0💬

Why does the simple line-copying loop while ...
Why does the simple line-copying loop while(!feof(infp)) { fgets(buf, MAXLINE, infp); fputs(buf, outfp); } copy the last line twice? p> In C, end-of-file is only indicated after an input routine has tried to read, and failed. (In other words, C's I/O is not like Pascal's.) Usually, you should just c... 2015-11-13, 1370👍, 0💬

Why doesnt the call scanf work?
Why doesn't the call scanf("%d", i) work? The arguments you pass to scanf must always be pointers: for each value converted, scanf ``returns'' it by filling in one of the locations you've passed pointers to. To fix the fragment above, change it to scanf("%d", &i) . 2015-11-02, 1369👍, 0💬

I am trying to sort an array of strings with qsort, using strcmp as the comparison function, but it is not working.
I am trying to sort an array of strings with qsort, using strcmp as the comparison function, but it is not working. By ``array of strings'' you probably mean ``array of pointers to char.'' The arguments to qsort's comparison function are pointers to the objects being sorted, in this case, pointers t... 2015-08-12, 1365👍, 0💬

Here is a neat trick for checking whether two strings are equal
Q: Here's a neat trick for checking whether two strings are equal: if(!strcmp(s1, s2)) Is this good style? It is not particularly good style, although it is a popular idiom. The test succeeds if the two strings are equal, but the use of ! (``not'') suggests that it tests for inequality. Another opti... 2015-05-15, 1365👍, 0💬

How can I generate floating-point random numbers?
How can I generate floating-point random numbers? drand48 is a Unix System V routine which returns floating point random numbers (presumably with 48 bits of precision) in the half-open interval [0, 1). (Its companion seed routine is srand48; neither is in the C Standard.) It's easy to write a low-pr... 2015-07-22, 1364👍, 0💬

What is Hungarian Notation? Is it worthwhile?
What is Hungarian Notation? Is it worthwhile? Hungarian Notation is a naming convention, invented by Charles Simonyi, which encodes information about a variable's type (and perhaps its intended use) in its name. It is well-loved in some circles and roundly castigated in others. Its chief advantage i... 2015-05-08, 1364👍, 0💬

What does the message Automatic aggregate intialization is an ANSI feature mean?
What does the message Automatic aggregate intialization is an ANSI feature'' mean? My compiler is complaining about valid ANSI code. Messages like these are typically emitted by pre-ANSI compilers which have been upgraded just enough to detect (but not properly translate) new C features which were i... 2015-11-30, 1363👍, 0💬

How can I do PEEK and POKE in C?
How can I access memory (a memory-mapped device, or graphics memory) located at a certain address? How can I do PEEK and POKE in C? Set a pointer, of the appropriate type, to the right number (using an explicit cast to assure the compiler that you really do intend this nonportable conversion): unsig... 2015-03-20, 1362👍, 0💬

If you cant modify string literals, why arent they defined as being arrays of const characters?
If you cant modify string literals, why arent they defined as being arrays of const characters? One reason is that so very much code contains lines like char *p = "Hello, world!"; which are not necessarily incorrect. These lines would suffer the diagnostic messages, but it's really any later attempt... 2016-01-06, 1361👍, 0💬

Where can I get an ANSI-compatible lint?
Where can I get an ANSI-compatible lint? Products called PC-Lint and FlexeLint are available from Gimpel Software. The Unix System V release 4 lint is ANSI-compatible, and is available separately (bundled with other C tools) from UNIX Support Labs or from System V resellers. Another ANSI-compatible ... 2015-05-05, 1359👍, 0💬

Is there a way to switch on strings?
Is there a way to switch on strings? Not directly. Sometimes, it's appropriate to use a separate function to map strings to integer codes, and then switch on those: #define CODE_APPLE 1 #define CODE_ORANGE 2 #define CODE_NONE 0 switch(classifyfunc(string)) { case CODE_APPLE: ... case CODE_ORANGE: ..... 2015-02-04, 1359👍, 0💬

I need a sort of an approximate strcmp routine ...
I need a sort of an approximate strcmp routine ... Q: I need a sort of an ``approximate'' strcmp routine, for comparing two strings for close, but not necessarily exact, equality. A:Some nice information and algorithms having to do with approximate string matching, as well as a useful bibliography, ... 2015-01-09, 1359👍, 0💬

How can I clear the screen? How can I print text in color? How can I move the cursor to a specific x, y position?
How can I clear the screen? How can I print text in color? How can I move the cursor to a specific x, y position? Such things depend on the terminal type (or display) you're using. You will have to use a library such as termcap, terminfo, or curses, or some system-specific routines, to perform these... 2015-04-27, 1358👍, 0💬

Why cant I pass a char to a function which expects a const char ?
Why cant I pass a char to a function which expects a const char ? You can use a pointer-to-T (for any type T) where a pointer-to-const-T is expected. However, the rule (an explicit exception) which permits slight mismatches in qualified pointer types is not applied recursively, but only at the top l... 2016-01-04, 1357👍, 0💬

Was 2000 a leap year?
Was 2000 a leap year? Q: Is (year % 4 == 0) an accurate test for leap years? (Was 2000 a leap year?) A: No, it's not accurate (and yes, 2000 was a leap year). The actual rules for the present Gregorian calendar are that leap years occur every four years, but not every 100 years, except that they do ... 2015-01-05, 1356👍, 0💬

Does C have an equivalent to Pascals with statement?
Does C have an equivalent to Pascals with statement? No. The way in C to get quick and easy access to the fields of a structure is to declare a little local structure pointer variable (which, it must be admitted, is not quite as notationally convenient as a with statement and doesn't save quite as m... 2015-01-14, 1355👍, 0💬

I am including the right header file for the library function I am using, but the linker keeps saying its undefined.
I am including the right header file for the library function I am using, but the linker keeps saying its undefined. In the general case of calling code in an external library, using #include to pull in the right header file(s) is only half of the story; you also have to tell the linker to search th... 2016-02-10, 1354👍, 0💬

Each time I run my program, I get the same sequence of numbers back from rand
Each time I run my program, I get the same sequence of numbers back from rand It's a characteristic of most pseudo-random number generators (and a defined property of the C library rand) that they always start with the same number and go through the same sequence. (Among other things, a bit of predi... 2015-07-29, 1354👍, 0💬

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.NET C C++ CSS DBA General HTML Java JavaScript JSP JUnit MySQL Networking Oracle Perl Perl PHP PL/SQL RSS Software QA SQL Server Struts Unix Windows XHTML XML