C and C++ code is generally pretty easy to make sense of. But there are a few oddities which can catch you out and can send you into an endless debugging exercise if you’re not careful. One such oddity is conditional evaluation. Consider the following code which keeps track of three numbers. Look through the [...]
Archive for the ‘C’ Category
C/C++ Gotcha – Conditional Evaluation
Posted: 28th December 2010 by Tim in C, C++Tags: C, condition, conditional, evaluation, gotcha, if, loop, programming, while
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Reading from a file in C
Posted: 31st October 2010 by Tim in CTags: C, fgets, file, file handling, getline, input, program, read, string
Reading data from a file is fairly common. The stdio.h provides us with a function, getline, which allows us to read lines from a file without worrying about buffer overflows and other memory corruption issues that C is famous for. The following code opens a file named “myfile.txt” and prints out each line with the [...]
The difference between stack and heap memory allocation
Posted: 11th August 2010 by Tim in C, C++, Software DevelopmentTags: alloc, allocation, C, coding, free, heap, malloc, memory, stack, stack overflow
A common question amongst coders new to C or C++ relates to the difference between stack and heap memory allocation. The answer lies in how the code is executed at the very lowest level. When a program is executed, each thread is allocated a limited amount of stack space. The stack holds information used by [...]
Pthreads are a simple and effective way of creating a multi-threaded application. This introduction to pthreads shows the basic functionality – executing two tasks in parallel and merging back into a single thread when the work has been done. First I’ll run through the basics of threading applications with pthreads. Multi-threaded applications allow two or [...]
Checking if a float is not a number (nan) in C / C++
Posted: 10th March 2010 by Tim in C, C++Tags: C, divide by zero, double, float, fraction, math, nan, not a number, zero
Occasionally you need to check whether a float is a valid number. There are times, such as when the number is read in to a function as an argument, when you can’t assume that the check has already been done. This check can be done using the isnan(number) function from math.h. For example: #include <math.h> [...]
Getting avr32-linux-gcc compiler on linux
Posted: 14th December 2009 by Tim in Bash, C, UbuntuTags: atmel, avr32, avr32-linux-gcc, buildroot, compile, gcc, platform
If you’re trying to compile C programs for Linux on an AVR32 architecture, you’re going to have to get the avr32-linux-gcc cross compiler. Note that you can’t use the avr32-gcc compiler, as this compiler makes programs which do not run on an operating system (ie: they talk to the system directly), which will not run [...]
PQexecParams example – PostgreSQL query execution with parameters
Posted: 19th November 2009 by Tim in C, PostgreSQLTags: C, coding, exec, parameter, PostgreSQL, programming, query
The PostgreSQL documentation states that PQexecParams can be called like so: PGresult *PQexecParams(PGconn *conn, const char *command, int nParams, const Oid *paramTypes, const char * const *paramValues, const int *paramLengths, const int *paramFormats, int resultFormat); There are two parts of this call which can be tricky to novice C and/or PostgreSQL users and aren’t explained [...]
Millisecond timer in C / C++
Posted: 18th October 2009 by Tim in C, C++Tags: C, code, coding, header, include, program, programming, time, timer
If you’re looking for a timer with fairly good accuracy in C or C++, you can use the functions in time.h and sys/time.h to build a millisecond timer. This is useful for things like evaluating the execution time of a program, roughly accurate to the nearest microsecond. double get_time_ms() { struct timeval t; gettimeofday(&t, NULL); [...]
Converting latitude and longitude into mercator (UTM) X and Y coordinates
Posted: 6th October 2009 by Tim in C, C++Tags: C, degrees, global, lat, latitude, lon, longitude, mercator, pi, position, utm
The following calculations have been sourced from the Navit Project source code, released under the GNU General Public License version 2. To convert latitude and longitude into UTM X and Y coordinates, we can simply perform two calculations (lat is latitude and lon is longitude): x = lon × 6371000.0 × pi รท 180 y [...]
Math theory tells us that doing logarithms to custom bases can be done in the following way: log[base n](x) = log(x) / log(n) we can do the same in C. For example, if we wanted to calculate log[base 2](x): #include <math.h> … double log_2 = log(x) / log(2.0); Be sure to compile with the -lm [...]
Nanosleep in C / C++
Posted: 29th September 2009 by Tim in C, C++Tags: C, call, coding, development, nanosleep, programming, sleep, software engineering, usleep
usleep is not a very accurate form of sleep in C / C++. From the man page: The sleep may be lengthened slightly by any system activity or by the time spent processing the call or by the granularity of system timers. nanosleep, on the other hand, is much more accurate. The following code will [...]
Connecting to MySQL in C
Posted: 20th August 2009 by Tim in C, MySQL, UbuntuTags: C, coding, compile, connectivity, database, development, gcc, MySQL, sockets, sql, Ubuntu
MySQL comes with a library to make talking to MySQL with C easyish. There are a few things you have to install first, though. I’m using Ubuntu 8.04 for this walkthrough, but things should be similar for other flavours of Linux. Before we start, we have to download the development files required: sudo apt-get install [...]
Baud rate and other serial comm settings in C
Posted: 4th August 2009 by Tim in CTags: baud, C, coding, comms, communication, networking, programming, rate, serial, settings
Communicating through a serial port in C is pretty simple once it’s set up; you just read and write to it as though it was a file. The setting up, however, can be a real pain. Here’s the short and simple way to get it done. Note that this code requires the following headers: #include [...]