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POdispatch_write() and dispatch_read() usage
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Id
17948903
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17970921
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1
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CreationDate
2013-07-30T13:48:41.297
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1
LastActivityDate
2013-07-31T13:00:28.907
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2013-07-30T20:00:00.773
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1256957
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1256957
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PostTypeId
1
Score
4
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1514
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text
Body
I'm just playing with some GCD functions for writing and reading data to files. Two of these functions are <code>dispatch_write()</code> and <code>dispatch_read()</code>, which allow one to write and read data to a file descriptor without having to setup a new <code>dispatch_io_t</code> channel. So, I have the following code: <pre><code>#import <dispatch/dispatch.h> #import <stdio.h> #import <unistd.h> int main() { dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); int intbuffer[] = { 1, 2, 3, 4 }; dispatch_data_t data = dispatch_data_create(intbuffer, 4 * sizeof(int), queue, NULL); // Write dispatch_fd_t fd = open("data.dat", O_RDWR); printf("FD: %d\n", fd); dispatch_write(fd, data, queue,^(dispatch_data_t d, int e) { printf("Written %zu bytes!\n", dispatch_data_get_size(d)); printf("\tError: %d\n", e); }); close(fd); // Read fd = open("data.dat", O_RDWR); dispatch_read(fd, 4 * sizeof(int), queue, ^(dispatch_data_t d, int e) { printf("Read %zu bytes!\n", dispatch_data_get_size(d)); printf("\tError: %d\n", e); }); close(fd); // Exit confirmation getchar(); return 0; } </code></pre> with which I'm attempting to write a 4-integer array to a file and, after that, to read it back. I previously created <code>data.dat</code> with the <code>touch</code> command and anyone has full access to it (<code>sudo chmod 777 data.dat</code>). When I execute this code, it seems <code>data.dat</code> gets open successfully, since the program prints out <code>FD: 3</code>, which is a valid file descriptor, but <code>dispatch_write</code> doesn't write anything to it, since I get: <pre><code>Written 0 bytes! Error: 9 Read 0 bytes! Error: 9 </code></pre> Error 9 is the code for a <code>EBADF</code> error, but, again, 3 is a valid file descriptor. So, what am I doing wrong?
Tags
<macos><file-io><grand-central-dispatch>
Title
dispatch_write() and dispatch_read() usage
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1. PO
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1. USLuisABOL
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1. USLuisABOL
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