fseek | 易学教程

Can fseek(stdin,1,SEEK_SET) or rewind(stdin) be used to flush the input buffer instead of non-portable fflush(stdin)?

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问题 Since I discovered fflush(stdin) is not a portable way to deal with the familiar problem of "newline lurking in the input buffer" ,I have been using the following when I have to use scanf : while((c = getchar()) != '\n' && c != EOF); But today I stumbled across this line which I had noted from cplusplus.com on fflush: fflush()...in files open for update (i.e., open for both reading and writting), the stream shall be flushed after an output operation before performing an input operation. This

Overwrite to a specific line in c

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问题 I have a file of about 2000 lines of text that i generate in my program, every line has the information of an employee and it's outputed like this 1 1 Isaac Fonseca 58 c 1600 1310.40 6 1 0.22 2164.80 1 2 1 Manuel Gutierrez 22 d 1700 1523.37 4 1 0.13 897.26 1 3 1 Daniel Bernal 34 c 1600 1195.84 2 1 0.26 836.16 1 4 1 Miguel Gonzalez 43 e 1800 1195.84 0 1 0.15 0.00 1 But i whenever i edit an employee information i have to update the file, what i'm doing it's i search for the line and try to

Matlab, fread, speed up reading file with multiple data types and multiple sample rates

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可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: Using Matlab R2015a. I'm using fread to read sensor data from a binary file. The data contains multiple precisions. One signal is sampled at 5 times the rate of the other signals. The file is structured as a sequence of batches, where each batch has e.g. 1 sample of signal_A, but 5 samples of signal_B. I have googled for examples on how to load and format the data fast, but the solutions I have seen only represent cases where there is a single sampling rate, making the solution simpler, as far as I can tell. What I would like to avoid is the

数据结构课设：高精度算法

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高精度算法，属于处理大数字的数学计算方法。在一般的科学计算中，会经常算到小数点后几百位或者更多，当然也可能是几千亿几百亿的大数字。一般这类数字我们统称为高精度数，高精度算法是用计算机对于超大数据的一种模拟加，减，乘，除，乘方，阶乘，开方等运算。对于非常庞大的数字无法在计算机中正常存储，于是，将这个数字拆开，拆成一位一位的，或者是四位四位的存储到一个数组中，用一个数组去表示一个数字，这样这个数字就被称为是高精度数。高精度算法就是能处理高精度数各种运算的算法，但又因其特殊性，故从普通数的算法中分离，自成一家。 . 由于计算机运算是有模运算,数据范围的表示有一定限制,如整型int(C++中int 与long相同)表达范围是(-2^31~2^31-1),unsigned long(无符号整数)是(0~2^32-1),都约为几十亿.如果采用实数型,则能保存最大的double只能提供15~16位的有效数字,即只能精确表达数百万亿的数.因此,在计算位数超过十几位的数时,不能采用现有类型,只能自己编程计算。 ―― [ 百度百科 ] 题目： ① 整数长度在一百位以上 ② 实现两长整数的加减乘除操作，除法要返回商和余数 ③ 输入输出均在文件中高精度计算时一般用一个数组来存储一个数,数组的一个元素对应于数的一位(当然,在以后的优化中为了加快计算速度,也可用数组的一个元素表示数的多位数字),表示时

Undoing the effects of ungetc() : “How” do fseek(),rewind() and fsetpos() do it?Is buffer refilled each time?

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问题 Huh!!How shall I put the whole thing in a clear question!!Let me try: I know that the files opened using fopen() are buffered into memory.We use a buffer for efficiency and ease.During a read from the file, the contents of the file are first read to the buffer,and we read from that buffer.Similarly,in a write to the file, the contents are written to the buffer first ,and then to the file. But what with fseek() , fsetpos() and rewind() dropping the effect of the previous calls to ungetc() ?

Will fseek function flush data in the buffer in C++?

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问题 We know that call to functions like fprintf or fwrite will not write data to the disk immediately, instead, the data will be buffered until a threshold is reached. My question is, if I call the fseek function, will these buffered data writen to disk before seeking to the new position? Or the data is still in the buffer, and is writen to the new position? cheng 回答1: I'm not aware if the buffer is guaranteed to be flushed, it may not if you seek to a position close enough. However there is no

Windows physical drive access fopen and fseek

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I'm currently trying to access a physical hard disk as a stream of binary data in C. I've mounted an image (.img), and it's readable from the OS (Win 7). My C program simply attempts to open the physical drive in read-only binary mode, then read some data from the drive. However, if I simply read data from the stream without seeking anywhere, all is well, I get back the data that is stored in the drive, and as I'm at offset 0 in the stream, I'm able to read the MBR on the disk. However, if I try to fseek to any offset from the origin (zero), fseek return -1, indicating that it couldn't do it.

need of fseek() in c

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Part of Code 1:- while(1) { ch=fgetc(pt); if(c==EOF) { break; } if(c==' ') { fputc('z',pt); } } Part of Code 2:- while(1) { ch=fgetc(pt); if(c==EOF) { break; } if(c==' ') { fseek(pt,0,SEEK_CUR); fputc('z',pt); fseek(pt,0,SEEK_CUR); } } I want to replace next character after every space in a file. That file is pointed by the pointer pt . Both the code shows no error and runs fine, but when I externally opens the .txt file, first code did nothing whereas the second code replaces the next character after space successfully. Clearly fseek(pt,0,SEEK_CUR); is making the difference. So I am unable to

need of fseek() in c

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问题 Part of Code 1:- while(1) { ch=fgetc(pt); if(c==EOF) { break; } if(c==' ') { fputc('z',pt); } } Part of Code 2:- while(1) { ch=fgetc(pt); if(c==EOF) { break; } if(c==' ') { fseek(pt,0,SEEK_CUR); fputc('z',pt); fseek(pt,0,SEEK_CUR); } } I want to replace next character after every space in a file. That file is pointed by the pointer pt . Both the code shows no error and runs fine, but when I externally opens the .txt file, first code did nothing whereas the second code replaces the next

Question about file seeking position

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My previous Question is about raw data reading and writing, but a new problem arised, it seems there is no ending.... The question is: the parameters of the functions like lseek() or fseek() are all 4 bytes. If i want to move a span over 4G, that is imposible. I know in Win32, there is a function SetPointer(...,Hign, Low,....) , this pointers can generate 64 byte pointers, which is what i want. But if i want to create an app in Linux or Unix (create a file or directly write the raw drive sectors), How can I move to a pointer over 4G? Thanx, Waiting for your replies... The offset parameter of