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How can I print numbers with commas separating the thousands? What about currency formatted numbers?
How can I print numbers with commas separating the thousands? What about currency formatted numbers? The functions in &lt;locale.h> begin to provide some support for these operations, but there is no standard C function for doing either task. (In Standard C, the only thing printf does in respons... 2015-11-02, 2223👍, 0💬

malloc is returning crazy pointer values ...
malloc is returning crazy pointer values, I have included the line extern void *malloc(); before I call it. malloc accepts an argument of type size_t, and size_t may be defined as unsigned long. If you are passing ints (or even unsigned ints), malloc may be receiving garbage (or similarly if you are... 2016-04-15, 2191👍, 0💬

Return a null pointer or a pointer to 0 bytes? .....
What should malloc(0) 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 ortable code must either take care not to call malloc(0), or be prepared for the possibility of a null return. 2016-04-21, 2160👍, 0💬

What's the best way to write a multi-statement macro?
What's the best way to write a multi-statement macro? The usual goal is to be able to invoke the macro as if it were an expression statement consisting of a function call: MACRO(arg1, arg2); This means that the ``caller'' will be supplying the final semicolon, so the macro body should not. The macro... 2016-02-22, 2104👍, 0💬

I need a random number generator.
I need a random number generator. The Standard C library has one: rand. The implementation on your system may not be perfect, but writing a better one isn't necessarily easy, either. Here is a portable C implementation of the ``minimal standard'' generator : #define a 16807 #define m 2147483647 #def... 2015-08-03, 2002👍, 0💬

My application depends heavily on dynamic allocation of nodes for data structures ......
My application depends heavily on dynamic allocation of nodes for data structures, and malloc/free overhead is becoming a bottleneck. What can I do ? One improvement, which is particularly attractive if all nodes are the same size, is to place unused nodes on your own free list, rather than actually... 2016-04-12, 1997👍, 0💬

What is the difference between ......
Q: What's the difference between const MAXSIZE = 100; and #define MAXSIZE 100 A preprocessor #define gives you a true compile-time constant. In C, const gives you a run-time object which you're not supposed to try to modify; ``const'' really means ``readonly''. 2015-12-22, 1989👍, 0💬

How can I read a single character from the keyboard without waiting for the RETURN key?
How can I read a single character from the keyboard without waiting for the RETURN key? How can I stop characters from being echoed on the screen as they're typed? Alas, there is no standard or portable way to do these things in C. Concepts such as screens and keyboards are not even mentioned in the... 2015-04-29, 1984👍, 0💬

What is the correct declaration of main?
What is the correct declaration of main? There are two valid declarations: int main(void) int main(int argc, char **argv) although they can be written in a variety of ways. The second parameter may be declared char *argv[] , you can use any names for the two parameters, and you can use old-style syn... 2015-12-22, 1898👍, 0💬

Does anyone have a tool for converting old-style C programs to ANSI C?
Does anyone have a tool for converting old-style C programs to ANSI C, or vice versa, or for automatically generating prototypes? Two programs, protoize and unprotoize, convert back and forth between prototyped and ``old style'' function definitions and declarations. (These programs do not handle fu... 2015-11-25, 1884👍, 0💬

I am allocating a large array for some numeric work ...
I'm allocating a large array for some numeric work, using the line double *array = malloc(300 * 300 * sizeof(double)); malloc isn't returning null, but the program is acting strangely, as if it's overwriting memory, or malloc isn't allocating as much as I asked for, or something.. Notice that 300 x ... 2016-04-15, 1870👍, 0💬

How can printf use f for type double, if scanf requires lf?
Someone told me it was wrong to use %lf with printf. How can printf use %f for type double, if scanf requires %lf? It's true that printf's %f specifier works with both float and double arguments Due to the ``default argument promotions'' (which apply in variable-length argument lists values of type ... 2015-11-06, 1811👍, 0💬

What is the difference between these initializations? ....
What is the difference between these initializations? char a[] = "string literal"; char *p = "string literal"; My program crashes if I try to assign a new value to p[i]. A string literal (the formal term for a double-quoted string in C source) can be used in two slightly different ways: 1. As the in... 2016-03-09, 1802👍, 0💬

Why can I only seem to malloc 640K or so?. .....
I've got 8 meg of memory in my PC. Why can I only seem to malloc 640K or so?. Under the segmented architecture of PC compatibles, it can be difficult to use more than 640K with any degree of transparency, especially under MS-DOS. 2016-04-12, 1789👍, 0💬

I have seen function declarations that look like this
I've seen function declarations that look like this: extern int func __((int, int)); What are those extra parentheses and underscores for? They're part of a trick which allows the prototype part of the function declaration to be turned off for a pre-ANSI compiler. Somewhere else is a conditional def... 2015-05-23, 1781👍, 0💬

How does free know how many bytes to free?
How does free know how many bytes to free? The malloc/free implementation remembers the size of each block as it is allocated, so it is not necessary to remind it of the size when freeing. (Typically, the size is stored adjacent to the allocated block, which is why things usually break badly if the ... 2016-03-24, 1780👍, 0💬

I im dynamically allocating an array, like this ...
I'm dynamically allocating an array, like this: int *iarray = (int *)malloc(nints); malloc isn't returning NULL, but the code isn't working. A:malloc is a low-level, typeless allocator. It doesn't know how you're going to use the memory; all it does is to allocate as many bytes of memory as you ask ... 2016-04-06, 1779👍, 0💬

People seem to make a point of distinguishing between ...
People seem to make a point of distinguishing between implementation-defined, unspecified, and undefined behavior. What do these mean? First of all, all three of these represent areas in which the C Standard does not specify exactly what a particular construct, or a program which uses it, must do. T... 2015-11-23, 1774👍, 0💬

How can I print a character in a printf format string?
How can I print a '%' character in a printf format string? I tried \%, but it didn't work. Simply double the percent sign: %% . The reason it's tricky to print % signs with printf is that % is essentially printf's escape character. Whenever printf sees a %, it expects it to be followed by a characte... 2015-11-09, 1774👍, 0💬

Why isn't a pointer null after calling free? ...
Why isn't a pointer null after calling free? How unsafe is it to use (assign, compare) a pointer value after it's been freed? When you call free, the memory pointed to by the passed pointer is freed, but the value of the pointer in the caller probably remains unchanged, because C's pass-by-value sem... 2016-04-04, 1772👍, 0💬

I am allocating structures which contain pointers to other dynamically ....
I'm allocating structures which contain pointers to other dynamically-allocated objects. When I free a structure, do I also have to free each subsidiary pointer? Yes. malloc knows nothing about structure declarations or about the contents of allocated memory; it especially does not know whether allo... 2016-03-31, 1772👍, 0💬

You cant use dynamically-allocated memory after you free it?
You cant use dynamically-allocated memory after you free it? No. Some early documentation for malloc stated that the contents of freed memory were ``left undisturbed,'' but this ill-advised guarantee was never universal and is not required by the C Standard. Few programmers would use the contents of... 2016-04-04, 1763👍, 0💬

What is the difference between calloc and malloc? ....
What's the difference between calloc and malloc? Which should I use? Is it safe to take advantage of calloc's zero-filling? Does free work on memory allocated with calloc, or do you need a cfree? calloc(m, n) is essentially equivalent to p = malloc(m * n); memset(p, 0, m * n); There is no important ... 2016-03-16, 1761👍, 0💬

How can I split up a string into whitespace-separated fields?
How can I split up a string into whitespace-separated fields? How can I duplicate the process by which main() is handed argc and argv? The only Standard function available for this kind of ``tokenizing'' is strtok, although it can be tricky to use and it may not do everything you want it to. (For in... 2015-08-17, 1756👍, 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