sizeof | 易学教程

C结构体之位域（位段）

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几篇较全面的位域相关的文章： http://www.uplook.cn/blog/9/93362/ C/C++位域(Bit-fields)之我见 C中的位域与大小端问题内存对齐全攻略–涉及位域的内存对齐原则本文主要对位域相关知识进行了一下梳理，参考如下： C语言中的位域史上最全的C位域总结 2 C结构体之位域（位段） C/C++中以一定区域内的位(bit)为单位来表示的数据成为位域，位域必须指明具体的数目。位域的作用主要是节省内存资源，使数据结构更紧凑。 1. 一个位域必须存储在同一个字节中，不能跨两个字节，故位域的长度不能大于一个字节的长度。如一个字节所剩空间不够存放另一位域时，应从下一单元起存放该位域。也可以有意使某位域从下一单元开始。例如： struct BitField { unsigned int a:4; //占用4个二进制位; unsigned int :0; //空位域,自动置0; unsigned int b:4; //占用4个二进制位,从下一个存储单元开始存放; unsigned int c:4; //占用4个二进制位; unsigned int d:5; //占用5个二进制位,剩余的4个bit不够存储4个bit的数据,从下一个存储单元开始存放; unsigned int :0; //空位域,自动置0; unsigned int e:4; /

音视频即时通讯开发中音频模式的采集

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在很多即时通讯应用中，会根据应用场景的不同，需要对音频输入源进行选择，不同的应用场景对应不同的音频工作模式。需要支持多种音频工作（采集）模式，包括： 1 、发言模式（默认）：自动选择麦克风为音频输入源设备，用户说话的声音被麦克风采集，启动音频特效处理（包括：回音消除、静音检测、噪音抑制、自动增溢），该模式通常应用于互动交流，用户发言讨论等场合； 2 、放歌模式：自动选择立体声混音输入源设备，本地计算机所播放的声音被采集，同时SDK内部会自动屏蔽其它用户的声音（如果不屏蔽，则用户的声音会被采集下来，并回传给用户，用户那边将会听到回音），SDK内部会自动关闭音频特效处理，该模式通常应用于向其他用户放歌，而不用关心其他用户发言的场合； 3 、卡拉OK模式：自动选择立体声混音和麦克风两个输入源设备（该特性与硬件相关，有些声卡不支持同时采集麦克风和立体声混音），本地计算机所播放的声音和用户说话的声音将会被采集，同时SDK内部会自动屏蔽其它用户的声音，SDK内部会自动关闭音频特效处理，该模式通常应用于向其他用户放歌，同时自己用麦克风伴唱，而不用关心其它用户发言的场合； 4 、线路输入模式：自动选择线路输入源设备，通过线路输入的声音将被采集（通常是指将外部的DV、DVD、TV等设备的音频输出端子接入声卡的LineIn口的应用），SDK内部会自动关闭音频特效处理

How does sizeof work for int types?

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问题 I have a small program which compares (1) sizeof, (2) numeric_limits::digits, (3) and the results of a loop in an effort to make sure they all report the same thing regarding the size of the "int types" on any C++ implementation. However because I don't know about the internals of sizeof, I have to wonder if it is just reporting numeric_limits::digits. Thanks 回答1: Most likely sizeof() on most compilers causes the compiler to look the given type (or object's type) up in its internal type table

How can I calculate the number of elements in a char array?

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问题 I was trying to calculate the number of elements in an array, and was told that the line int r = sizeof(array) / sizeof(array[0]) would give me the number of elements in the array. And I found the method does work, at least for int arrays. When I try this code, however, things break. #include <iostream> #include <Windows.h> using namespace std; int main() { char binaryPath[MAX_PATH]; GetModuleFileName(NULL, binaryPath, MAX_PATH); cout << "binaryPath: " << binaryPath << endl; cout << "sizeof

sizeof an integer expression in C

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问题 To my semi-surprise with Xcode compiling C (gnu11) #include <stdio.h> int main(int argc,char**argv) { short s = 1; printf( "%zd %zd %zd\n", sizeof(s), sizeof(s*s), sizeof(s?s:s)); return 0; } Produces the output 2 4 4 I was expecting 2 2 2 or possibly 2 4 2 Why is this? 回答1: I recalled from K&R that any integer expression smaller than an int is promoted to int. I found this in Standard (C89): 3.2.1.1 Characters and integers A char, a short int, or an int bit-field, or their signed or unsigned

How to get the size of an object via reference?

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问题 Suppose I have a class class Foo { : : } I have another function void getf( Foo &f) { : : std::cout<<sizeof f<<std::endl; } After I process the data and assign a lot of data to f (vector included in Foo members), I need the size of f object However, as what I did above, I always get 16, which is the size of a reference here. Did I do anything wrong? How to do that? Thanks! 回答1: sizeof returns the size of a type. Often time, as in the case of a Vector , the size of the type does not

C++: size of a char array using sizeof

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问题 Look at the following piece of code in C++: char a1[] = {'a','b','c'}; char a2[] = "abc"; cout << sizeof(a1) << endl << sizeof(a2) << endl; Though sizeof(char) is 1 byte, why does the output show sizeof(a2) as 4 and not 3 (as in case of a1 )? 回答1: C-strings contain a null terminator, thus adding a character. Essentially this: char a2[] = {'a','b','c','\0'}; 回答2: That's because there's an extra null '\0' character added to the end of the C-string, whereas the first variable, a1 is an array of

sizeof的内部实现

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#define sizeof(type) ((size_t) ((type*)0 + 1)) 来源： CSDN 作者： iot橘子皮链接： https://blog.csdn.net/weixin_41939983/article/details/103795168

What arguments does the sizeof operator take in C?

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问题 [ Original title referred to 'sizeof function'. ] I tried these and they all worked: char *p; printf("Size of *p is %d\n",sizeof(*p)); //result =1 printf("Size of p is %d\n",sizeof( p)); //result =4 printf("Size of p is %d\n",sizeof(&p)); //result =4 I wonder why the first printf is 1, the 2nd and 3rd is 4? So what arguments can sizeof can actually take? 回答1: It takes a type. sizeof(char) is always one. The variable p itself is a pointer, and on your platform that has a size of 4. Then you do

What's the size of this C# struct?

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问题 Is it 12 bytes or 16 bytes when stored in a List<DataPoint> ? public struct DataPoint { DateTime time_utc; float value; } Is there any sizeof function in C#? 回答1: Take a look at @Hans Passant's answer here for interesting background on this issue, esp. with regard to the limitations of Marshal.Sizeof . 回答2: Marshal.SizeOf() http://msdn.microsoft.com/en-us/library/y3ybkfb3.aspx 回答3: The CLR is free to lay out types in memory as it sees fit. So it's not possible to directly give "the" size.