fread

fread Function in C Programming

由 戏子无情 提交于 2019-12-10 03:46:50
问题 I have two questions about C's fread function: I have read that fread is used to read a binary file. However, when I read a binary file with fgets using read mode "r" and a text file with fread using "rb" mode, the results are the same as reading a text file with fgets and a binary file with fread . So, why are there different functions for reading binary and text files? I am using fread to read 10 bytes of a file in one call. How should I stop reading at the end of file – i.e. how is EOF

What's the intended use of _fread_nolock, _fseek_nolock?

由 久未见 提交于 2019-12-08 09:14:14
问题 we have a C++ class which basically reads and writes vectors from a binary file. An exemplary read function that loads a single vector into memory looks like this: int load (const __int64 index, T* values) const { int re = _fseeki64(_file, index * _vectorSize + _offsetData, SEEK_SET); assert(re == 0); size_t read = fread(values, sizeof(T), _vectorElements, _file); assert(read == _vectorElements); return 0;} Out programs are multithreaded with OpenMP and multiple threads access the same file

using fread to read into int buffer

由 家住魔仙堡 提交于 2019-12-08 03:59:52
问题 I would like to know if I can use fread to read data into an integer buffer. I see fread() takes void * as the first parameter. So can't I just pass an integer buffer (typecast to void *) and then use this to read howmuchevery bytes I want to from the file, as long as the buffer is big enough ? ie. cant i do: int buffer[10]; fread((void *)buffer, sizeof(int), 10, somefile); // print contents of buffer for(int i = 0; i < 10; i++) cout << buffer[i] << endl; What is wrong here ? Thanks 回答1: This

how fread works in C?

由 橙三吉。 提交于 2019-12-08 02:03:10
问题 I have text file with content as: 12345678901222344567 Then I used this code to read the content: FILE * pFile; int c; char buffer [256]; pFile = fopen ("myfile.txt","r"); int a[50] = {0}; fread(a, sizeof(a[0]), 5, pFile); fclose(pFile); for (c = 0; c < 5; c++) { printf("%d\n", a[c]); } and I got the results: I cannot explain myself why I got such results. 回答1: Text file vs. Binary file You misuse the fread function on a text file which is supposed to be used on a binary file. A text file is

Using fread/fwrite for STL string. Is it correct?

由 |▌冷眼眸甩不掉的悲伤 提交于 2019-12-07 08:42:47
问题 I have a structure, that contain string. Something like that: struct Chunk { int a; string b; int c; }; So, i suppose, that i cannot write and read this structure from file using fread and fwrite functions. Because string may reserve different memory capacity. But such code works correctly. Chunk var; fwrite(&var, sizeof(Chunk), 1, file); fread(&var, sizeof(Chunk), 1, file); Is there really some problems in it? 回答1: You are justified in doubting this. You should only stream POD types with

using fread to read into int buffer

由 蹲街弑〆低调 提交于 2019-12-07 08:30:27
I would like to know if I can use fread to read data into an integer buffer. I see fread() takes void * as the first parameter. So can't I just pass an integer buffer (typecast to void *) and then use this to read howmuchevery bytes I want to from the file, as long as the buffer is big enough ? ie. cant i do: int buffer[10]; fread((void *)buffer, sizeof(int), 10, somefile); // print contents of buffer for(int i = 0; i < 10; i++) cout << buffer[i] << endl; What is wrong here ? Thanks This should work if you wrote the ints to the file using something like fwrite ("binary" write). If the file is

fread - read all columns as character

由 主宰稳场 提交于 2019-12-07 06:17:09
问题 I'm trying to read a file into R using data.table / fread . Some of the fields have leading zeros and I just want to read the data in as characters and manually fix them. However I can't figure out how to convey this to fread . I'm trying this and it's assigning char, num, etc types as it normally would : prop1 <- data.frame(fread("C:\\myFile.csv"), stringsAsFactors = F, colClasses = c(rep('character',58))) What am I missing? 回答1: Your colClasses argument is in the wrong place. It needs to be

fread is signalling EOF prematurely with a binary file

由 老子叫甜甜 提交于 2019-12-06 21:13:45
I'm a newcomer to C. I'm attempting to make my own version of base64 ; the program takes input from stdin and outputs its base64 equivalent to stdout. While testing my program against a binary file, I noticed that fread -ing from stdin seemed to be returning a short count early before actually reaching EOF. Here is the relevant portion of my main method: int main(void) { unsigned char buffer[BUFFER_SIZE]; unsigned char base64_buffer[BASE64_BUFFER]; while (1) { TRACE_PUTS("Reading in data from stdin..."); size_t read = fread(buffer, 1, sizeof(buffer), stdin); /* Read the data in using fread(3)

C reading/writing to a file in binary mode

由 自闭症网瘾萝莉.ら 提交于 2019-12-06 15:37:45
问题 I created a File of 4000 blocks with a blocksize of 4096 Bytes. Now I want to manipulate single blocks and read them again without changeing the files' size. Actually I want to write blocks out of another file to specific blocks in the file I created. Therefore I am opening the Files in binarymode like this: FILE * storeFile=fopen(targetFile, "wb"); // this one I created before FILE * sourceFILE=fopen(sourceFile,"rb"); now I am trying to read stuff to a pointer char * ptr=malloc(4096); ...

how fread works in C?

由 ε祈祈猫儿з 提交于 2019-12-06 13:27:09
I have text file with content as: 12345678901222344567 Then I used this code to read the content: FILE * pFile; int c; char buffer [256]; pFile = fopen ("myfile.txt","r"); int a[50] = {0}; fread(a, sizeof(a[0]), 5, pFile); fclose(pFile); for (c = 0; c < 5; c++) { printf("%d\n", a[c]); } and I got the results: I cannot explain myself why I got such results. Text file vs. Binary file You misuse the fread function on a text file which is supposed to be used on a binary file. A text file is different with a binary file . Let's say, if you save txt with four ASCII characters "1" , "2" , "3" , "4" ,
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