Recent questions tagged C

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c - printf and %llx in GCC under Windows 64x

I am trying to get rid of a bogus warning in my program. Under windows 64 (under linux there is no such ... a correct and non-sloppy way. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - Iterate through Lua Table

I am trying to iterate through a lua table but I keep getting this error: invalid key to 'next' I know ... , could this be disrupting lua_next? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - putchar() vs printf() - Is there a difference?

I am currently in chapter 1.5.1 File copying and made a program like so: #include <stdio.h> /* copy input to ... is better to use between the 2? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - popen implicitly declared even though #include <stdio.h> is added

This is tiny snippet of my code. #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <time.h ... because its an a assignment). See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - implicit declaration of function itoa is invalid in c99

When I try use the function itoa(), I get the warning: implicit declaration of function is invalid in c99. I ... not sure if this is allowed. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - Is it necessary to multiply by sizeof( char ) when manipulating memory?

When using malloc and doing similar memory manipulation can I rely on sizeof( char ) being always 1? For ... ever necessary for char type? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - What happens to Mutex when the thread which acquired it exits?

Suppose there are two threads, the main thread and say thread B(created by main). If B acquired a mutex(say ... the mutex? Does it become free? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - Treating __func__ as a string literal instead of a predefined identifier

I am using gcc to compile C99 code. I want to write a macro which will return a string containing the ... __func__ macro in my string? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - Possible Memory Leak Valgrind in OSX El Capitan

I'm getting a warning for possibly lost: 2,064 bytes in 1 blocks when using Valgrind on OSX Yosemite. Is ... contexts (suppressed: 17 from 17) See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - Massive fprintf speed difference without "-std=c99"

I had been struggling for weeks with a poor-performing translator I had written. On the following simple bechmark ... that makes it so slow. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - Does fprintf use malloc() under the hood?

I want a minimal o-damn-malloc-just-failed handler, which writes some info to a file (probably just standard error ... fprintf won't do this? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - Is sscanf considered safe to use?

I have vague memories of suggestions that sscanf was bad. I know it won't overflow buffers if I use the ... memory just playing tricks with me? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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546 views

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c preprocessor - How efficient is define in PHP?

C++ preprocessor #define is totally different. Is the PHP define() any different than just creating a var? define ... 0; $something = $setting; See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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511 views

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c - GDB says "no symbol table," but nm shows file has debug symbols

I'm trying to debug a simple C project using GDB, but GDB can't seem to find the debug symbols for the ... my GDB is the "wrong" version? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - Passing pointer to local variable to function: is it safe?

For example: void func1(){ int i = 123; func2(&i); } void func2(int *a){ *a = 456; } When func1 ... this safe for the rules of C? Thanks. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - Getting the source address of an incoming socket connection

I have a server with a incoming socket from a client. I need the get the IP address of the remote ... a bit troublesome. Any suggestions? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - Why does gcc allow extern declarations of type void (non-pointer)?

Why does gcc allow extern declarations of type void? Is this an extension or standard C? Are there acceptable uses ... use of type 'void' See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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420 views

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c - Variables declared inside a loop

If I were to declare a variable inside of a loop, is it faster to have the declaration outside of the loop? Does the ... ); printf("%d ",n); } See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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666 views

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c - What does GCC __attribute__((mode(XX)) actually do?

This arose from a question earlier today on the subject of bignum libraries and gcc specific hacks to the C language ... systems, am I correct? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - How to print types of unknown size like ino_t?

I often experience situations where I want to print with printf the value of an integer type of implementation- ... there a better strategy? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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625 views

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c - How does the internal implementation of memcpy work?

How does the standard C function 'memcpy' work? It has to copy a (large) chunk of RAM to another area in ... RAM. Apparently this isn't true. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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487 views

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c - Is sending data via UDP sockets on the same machine reliable?

If i use UDP sockets for interprocess communication, can i expect that all send data is received by the other ... true for UDP in general. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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566 views

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c - cast variable to int vs round() function

I have seen it in several places where (int)someValue has been inaccurate and instead the problem called for the ... when writing them in java. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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590 views

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c - Does malloc reserve more space while allocating memory?

I am observing the following behavior in my test program: I am doing malloc() for 1 MB and then free( ... some reserve while allocating memory? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - How do I retrieve an error string from WSAGetLastError()?

I'm porting some sockets code from Linux to Windows. In Linux, I could use strerror() to convert an ... -readable error strings from Winsock? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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808 views

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c - How to circumvent format-truncation warning in GCC?

I'm getting the following gcc format-truncation warning: test.c:8:33: warning: /input' directive output may be ... or -Wno-format-truncation)? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c - Should I free/delete char* returned by getenv()?

char * val; val = getenv("ENV_VAR_NAME"); above is a code to get environment variable, will it cause memory ... If no then please answer why? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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502 views

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c - Bizarre use of conditional operator in Linux

In the 3.0.4 Linux kernel, mm/filemap.c has this line of code: retval = retval ?: desc.error; I've ... describes this behavior. Why is this OK? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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