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Suggesting that there can be 62 seconds in a minute?
Suggesting that there can be 62 seconds in a minute? Q: Why can tm_sec in the tm structure range from 0 to 61, suggesting that there can be 62 seconds in a minute? A: That's actually a buglet in the Standard. There can be 61 seconds in a minute during a leap second. It's possible for there to be two... 2015-01-05, 1717👍, 0💬

I am appalled that the ANSI Standard leaves so many issues undefined ...
I'm appalled that the ANSI Standard leaves so many issues undefined. Isn't a Standard's whole job to standardize these things? It has always been a characteristic of C that certain constructs behaved in whatever way a particular compiler or a particular piece of hardware chose to implement them. Thi... 2015-11-18, 1716👍, 0💬

How can I add N days to a date? How can I find the difference between two dates?
How can I add N days to a date? How can I find the difference between two dates? The ANSI/ISO Standard C mktime and difftime functions provide some (limited) support for both problems. mktime accepts non-normalized dates, so it is straightforward to take a filled-in struct tm, add or subtract from t... 2015-08-05, 1716👍, 0💬

Why is the macro giving me the warning
Why is the macro #define TRACE(n) printf("TRACE: %d\n", n) giving me the warning ``macro replacement within a string literal''? It seems to be expanding TRACE(count); as printf("TRACE: %d\count", count); Some pre-ANSI compilers/preprocessors interpreted macro definitions like #define TRACE(var, fmt)... 2016-01-25, 1711👍, 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, 1709👍, 0💬

I have an old macro that doesn't seem to work any more....
I have an old macro #define CTRL(c) ('c' &amp; 037) that doesn't seem to work any more. The intended use of this macro is in code like tchars.t_eofc = CTRL(D); which is expected to expand to tchars.t_eofc = ('D' &amp; 037); based on the assumption that the actual value of the parameter c wil... 2016-01-25, 1707👍, 0💬

What's the difference between...?
What's the difference between #include &lt;> and #include "" ? The syntax is typically used with Standard or system-supplied headers, while "" is typically used for a program's own header files. 2016-02-16, 1706👍, 0💬

Is if(p), where p is a pointer, a valid and portable test?
Is if(p), where p is a pointer, a valid and portable test? It is always valid. When C requires the Boolean value of an expression, a false value is inferred when the expression compares equal to zero, and a true value otherwise. That is, whenever one writes if(expr) where ``expr'' is any expression ... 2016-02-29, 1705👍, 0💬

Should I use symbolic names like TRUE and FALSE for Boolean constants, or plain 1 and 0?
Should I use symbolic names like TRUE and FALSE for Boolean constants, or plain 1 and 0? It's your choice. Preprocessor macros like TRUE and FALSE (and, of course, NULL) are used for code readability, not because the underlying values might ever change. It's a matter of style, not correctness, wheth... 2015-05-11, 1705👍, 0💬

Why is p turning out const, instead of the characters pointed to?
I've got the declarations typedef char *charp; const charp p; Why is p turning out const, instead of the characters pointed to? typedef substitutions are not purely textual.In the declaration const charp p; p is const for the same reason that const int i declares i as const. The typedef'ed declarati... 2016-01-04, 1704👍, 0💬

How can I read a directory in a C program?
How can I read a directory in a C program? See if you can use the opendir and readdir functions, which are part of the POSIX standard and are available on most Unix variants. Implementations also exist for MS-DOS, VMS, and other systems. (MS-DOS also has FINDFIRST and FINDNEXT routines which do esse... 2015-04-01, 1703👍, 0💬

People keep saying that the behavior of ...
People keep saying that the behavior of i = i++ is undefined, but I just tried it on an ANSI-conforming compiler, and got the results I expected. A compiler may do anything it likes when faced with undefined behavior (and, within limits, with implementation-defined and unspecified behavior), includi... 2015-11-18, 1702👍, 0💬

I thought that using large model meant that I could use more than 64K of data!
What does the error message ``DGROUP data allocation exceeds 64K'' mean, and what can I do about it? I thought that using large model meant that I could use more than 64K of data! Even in large memory models, MS-DOS compilers apparently toss certain data (strings, some initialized global or static v... 2015-03-20, 1702👍, 0💬

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 ol... 2015-03-09, 1700👍, 0💬

What are near and far pointers?
What are near and far pointers? These days, they're pretty much obsolete; they're definitely system-specific. They had to do with 16-bit programming under MS-DOS and perhaps some early versions of Windows. If you really need to know, see a DOS- or Windows-specific programming reference. If you're us... 2015-03-02, 1700👍, 0💬

How can f be used for both float and double arguments in printf? Aren't they different types?
How can f be used for both float and double arguments in printf? Aren't they different types? In the variable-length part of a variable-length argument list, the ``default argument promotions'' apply: types char and short int are promoted to int, and float is promoted to double. (These are the same ... 2015-06-17, 1698👍, 0💬

What is alloca and why is its use discouraged?
What is alloca and why is its use discouraged? alloca allocates memory which is automatically freed when the function which called alloca returns. That is, memory allocated with alloca is local to a particular function's ``stack frame'' or context. alloca cannot be written portably, and is difficult... 2016-03-14, 1697👍, 0💬

How can I read in an object file and jump to locations in it?
How can I read in an object file and jump to locations in it? You want a dynamic linker or loader. It may be possible to malloc some space and read in object files, but you have to know an awful lot about object file formats, relocation, etc., and this approach can't work if code and data reside in ... 2015-03-09, 1695👍, 0💬

When I read numbers from the keyboard with scanf ...
When I read numbers from the keyboard with scanf and a "%d\n" format, like this: int n; scanf("%d\n", &amp;n); printf("you typed %d\n", n); it seems to hang until I type one extra line of input. Perhaps surprisingly, \n in a scanf format string does not mean to expect a newline, but rather to re... 2015-10-23, 1693👍, 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, 1693👍, 0💬

This program runs perfectly on one machine ...
This program runs perfectly on one machine, but I get weird results on another. Stranger still, adding or removing a debugging printout changes the symptoms... Lots of things could be going wrong; here are a few of the more common things to check: * uninitialized local variables integer overflow, es... 2015-05-27, 1692👍, 0💬

How can I ensure that integer arithmetic doesnt overflow?
How can I ensure that integer arithmetic doesnt overflow? The usual approach is to test the operands against the limits in the header file &lt;limits.h> before doing the operation. For example, here is a ``careful'' addition function: int chkadd(int a, int b) { if(INT_MAX - b &lt; a) { fputs... 2015-03-04, 1691👍, 0💬

Why cant I perform arithmetic on a void pointer?
Why cant I perform arithmetic on a void pointer? The compiler doesn't know the size of the pointed-to objects. (Remember that pointer arithmetic is always in terms of the pointed-to size; Therefore, arithmetic on void *'s is disallowed (though some compilers allow it as an extension). Before perform... 2015-12-07, 1689👍, 0💬

I am still getting errors due to library functions being undefined
I'm still getting errors due to library functions being undefined, even though I'm explicitly requesting the right libraries while linking. Many linkers make one pass over the list of object files and libraries you specify, and extract from libraries only those modules which satisfy references which... 2015-07-14, 1689👍, 0💬

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