fread

问题 Does fread have a limit for the number of bytes it can read at once? Or I can read any size I would like to charge in to my pointer? For example, Can I read file of 50MB once using fread to charge it into char pointer? 回答1: Theoretically, yes, it can read any number of bytes up to the maximum of size_t (which is an unsigned int (roughly 4GB on a 32-bit system). However, since your buffer will have to be allocated in a contiguous block, it is not likely to be feasible, nor advisable, to read

问题 I have a struct like that struct Data { int ID; double test_sample[2065][1]; int XX_row; int XX_col double **XX; //size=[2065][changing] double **alpha_new; //size=[changing][1] int alpha_new row; int alpha_new_col; double t3; double kernel_par; }person[20]; I've written this struct for every person (for 20 person) into 20 file using fwrite : fwrite(&person, sizeof( struct Data ), 1,Ptr ); Now I have 20 files in binary. Each file includes these variables for one person. All is Ok for now.

问题 Is there a getline function that uses fread (block I/O) instead of fgetc (character I/O)? There's a performance penalty to reading a file character by character via fgetc . We think that to improve performance, we can use block reads via fread in the inner loop of getline . However, this introduces the potentially undesirable effect of reading past the end of a line. At the least, this would require the implementation of getline to keep track of the "unread" part of the file, which requires

问题 This is my working code: size_t FileReader::Read(ByteVector& output) { output.resize(m_elementSize * m_blockSize); size_t read = fread(&output[0], m_elementSize, m_blockSize, m_file); output.resize(read); return read; } However previous I have tried code which had output.reserve(m_elementSize * m_blockSize); As far as I know reserve just founds place in memory for container. resize do the same, also changes memory from trash to some given values and change container size. fread first

问题 This question already has answers here : Writing and reading (fwrite - fread) structures with pointers (3 answers) Closed 4 years ago . gcc (GCC) 4.7.0 c89 Hello, I have the following structure that I am trying to fwrite and fread. However, because my device and resource are pointers. The fwrite will read the pointer values and not the data. I cannot use a array for the device or resource. Only pointers as they have to be dynamically allocated. I allocate all memory for the structure elements

问题 I've got a problem when checking for a response error after sending a Push Notification. This is my setup: From my PHP server, I'm sending Push Notifications. These notifications are send in the enhanced format, so I can get an error response from the Apple server. For example: Error #7 "Invalid payload size". The way I check for errors is reading the socket response: const ERROR_RESPONSE_SIZE = 6; $errorResponse = @fread($this->_apnsSocket, self::ERROR_RESPONSE_SIZE); This works fine when

问题 So I have a very simple program that reads the 3 first bytes of a file: int main(void) { FILE *fd = NULL; int i; unsigned char test = 0; fd = fopen("test.bmp", "r"); printf("position: %ld\n", ftell(fd)); for (i=0; i<3; i++) { fread(&test, sizeof (unsigned char), 1, fd); printf("position: %ld char:%X\n", ftell(fd), test); } return (0); } When I try it with a text file it works fine: position: 0 position: 1 char: 61 position: 2 char: 62 position: 3 char: 63 but when I run it with a PNG for

问题 I want to be able to read in a Windows text file, modify it in memory, and then overwrite the old file with the modified data. However, fread doesn't seem to store the carriage returns present in my Windows text file, which is throwing things off when I write over the old data. I can't find anyone else who seems to have had this issue. Here is some example code that demonstrates the problem: #include <stdio.h> #include <stdlib.h> int main() { FILE* textFile; long fileSize; char

问题 I'm getting a very strange error while trying to read from a simple text file with c fread() call. I made a very simple program to show that error: int main(int argc ,char ** argv) { FILE* fh = fopen("adult.txt","r"); if(fh==NULL){ printf("error opening file\n"); exit(0); } int s = 1000; printf("cur before=%d\n",ftell(fh)); char* b = malloc (sizeof(char)*s); int k =fread(b,sizeof(char),s,fh); printf("cur after reading %d bytes =%d\n",k,ftell(fh)); return EXIT_SUCCESS; } And what I get as

问题 I'm getting a very strange error while trying to read from a simple text file with c fread() call. I made a very simple program to show that error: int main(int argc ,char ** argv) { FILE* fh = fopen("adult.txt","r"); if(fh==NULL){ printf("error opening file\n"); exit(0); } int s = 1000; printf("cur before=%d\n",ftell(fh)); char* b = malloc (sizeof(char)*s); int k =fread(b,sizeof(char),s,fh); printf("cur after reading %d bytes =%d\n",k,ftell(fh)); return EXIT_SUCCESS; } And what I get as