Recent questions tagged C

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c - What's the most efficient way to load and extract 32 bit integer values from a 128 bit SSE vector?

I'm trying to optimize my code using SSE intrinsics but am running into a problem where I don't know of a good ... .2. Thanks for all your help. 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 - gcc, uninitialized global variables

Is there any way to know / warn if a global variable is uninitialized with gcc ? I got it for local/ atomic variables “-Wuninitialized” 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 - Error due to #include<graphics.h>

I am trying to compile a program which includes the graphics.h header file for C. I have added the graphics. ... these instead of graphics.h? 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 - Divide a signed integer by a power of 2

I'm working on a way to divide a signed integer by a power of 2 using only binary operators (<< >> + ^ ~ & | ... n) + ~0 part. How can it work? 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 - MPI Spawn: root process does not communicate to child processes

(Beginner question) I'm trying to spawn processes dynamically using MPI_Comm_Spawn and then broadcast a message to ... Hidra Process Manager. 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 - Bitwise OR of constants

While reading some documentation here, I came across this: unsigned unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit ... a good explanation? 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 mmap() fail with ENOMEM on a 1TB sparse file?

I've been working with large sparse files on openSUSE 11.2 x86_64. When I try to mmap() a 1TB sparse file, it ... } close(fd); return 0; } 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 - gdb macro symbols not present even when using -g3 or -ggdb3 or -gdwarf-4

I have this C file (sample.c): #include <stdio.h> #define M 42 #define ADD(x) (M + x) int main () ... gdb site. What am I doing wrong? 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 use read() to read data until the end of the file?

I'm trying to read binary data in a C program with read() but EOF test doesn't work. Instead it keeps running forever ... ", i); } close(fd); } 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 - in lex how to make yyin point to a file with the main function in yacc?

I am storing the arguments passed to main in yacc in a file. Now I want the lex to read its ... suggest something to overcome this problem. 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 - EVP_MD_CTX "error: storage size of ‘ctx’ isn’t known"

My system is Ubuntu16.04 LTS. when I use the OpenSSL EVP_MD_CTX, this error appeared. Can anyone help me? ... t known EVP_MD_CTX md_ctx,md_ctx2; 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 - Override weak symbols in static library

I want to make a static .a library for my project from multiple sources, some of them define weak functions and ... arm-none-eabi-gcc v4.8 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 detect Linux shutdown/reboot

I'm trying to detect shut down or reboot from Linux in my c program. I found that program can use signal( ... . Thanks for the great solution. 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 - Access command line arguments without using char **argv in main

Is there any way to access the command line arguments, without using the argument to main? I need to access it in ... Mac OS and Linux with GCC. 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 - casting into a Python string from a char[] returned by a DLL

I am attempting to cast a C style const char[] string pointer (returned from a DLL) into a Python compatible ... doing what it should be doing? See Question&Answers more detail:os...

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

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558 views

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c - Floating-point precision when moving from i386 to x86_64

I have an application that was developed for Linux x86 32 bits. There are lots of floating-point operations and ... need the 80 bit precision. 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 - Declaration of variable causes segmentation fault

I don't understand the reason for a segmentation fault error in my program. The code is available here At line ... crashes. Can anyone help 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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c - Get Assembly code after every optimization GCC makes?

From Optimization Compiler on Wikipedia, Compiler optimization is generally implemented using a sequence of optimizing ... be C code. 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 is the size of a variable length array computed at runtime in C99?

In C89, the length of an array is known at compile time. But in C99, with variable length arrays, the length ... be computed in the same 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 - Read/write from file descriptor at offset

I've been using the read(2) and write(2) functions to read and write to a file given a file descriptor. ... into the file for read/write? 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 - fscanf and newline character

I have fscanf to read lines of setting from a configuration file. Those settings have strictly predefined format ... more than once anywhere. See Question&Answers more detail:os...

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

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961 views

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c - When does printf fail to print?

printf function in c doesn't always print the output on screen. For example if you forget to put at the end ... . Can you guys please help. 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's the difference between the macros "#define STR(x) #x" and "#define STR(x) VAL(x)" with "#define VAL(x) #x"?

When I use this code: #include <stdio.h> #define STR(x) #x int main(void) { printf(__FILE__ STR(__LINE__) "hello! ... ) VAL(x) #define VAL(x) #x 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 there a gcc flag to initialise local variable storage?

The IBM AIX xlc compiler offers a flag that generates code to initialise local variable storage: initauto=<hh> ... equivalent option for GCC? See Question&Answers more detail:os...

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

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670 views

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c - Determine optimization level in preprocessor?

-Og is a relatively new optimization option that is intended to improve the debugging experience while apply ... use with the preprocessor? 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 - Why didn't the compiler warn me about an empty if-statement?

I'm using Keil uVision v4.74 and have enabled the option "All Warnings". I wrote the following intentional code: ... as a warning and inform 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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c - Why does gcc reorder the local variable in function?

I wrote a C program that just read/write a large array. I compiled the program with command gcc -O0 program.c - ... 5d pop %rbp 4008f5: c3 retq See Question&Answers more detail:os...

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

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755 views

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c - Non Blocking Socket

A non blocking socket is the one where we call fcntl() method and associate the O_NONBLOCK flag with it. ... very well with Windows servers? See Question&Answers more detail:os...

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

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