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Given the current outbreak of Coronavirus Disease 2019 (COVID-19) disease caused by the novel coronavirus SARS-CoV-2, consumers may be interested in purchasing ultraviolet-C (UVC) lamps to disinfect surfaces in the home or similar spaces. The FDA is providing answers to consumers’ questions about the use of these lamps for disinfection during the COVID-19 pandemic.

In this article, let us discuss how to debug a c program using gdb debugger in 6 simple steps. Write a sample C program with errors for debugging purpose. To learn C program debugging, let us create the following C program that calculates and prints the factorial of a number. However this C program contains some errors in it for our debugging. Download the Microsoft Visual C Redistributable for Visual Studio 2015, 2017 and 2019. The following updates are the latest supported Visual C redistributable packages for Visual Studio 2015, 2017 and 2019. Included is a baseline version of the Universal C Runtime see MSDN for details. X86: vcredist.x86.exe. X64: vcredist.x64.exe.

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Ultraviolet Radiation and SARS-CoV-2 Coronavirus

Q: Can UVC lamps inactivate the SARS-CoV-2 coronavirus?

A: UVC radiation is a known disinfectant for air, water, and nonporous surfaces. UVC radiation has effectively been used for decades to reduce the spread of bacteria, such as tuberculosis. For this reason, UVC lamps are often called 'germicidal' lamps.

UVC radiation has been shown to destroy the outer protein coating of the SARS-Coronavirus, which is a different virus from the current SARS-CoV-2 virus. The destruction ultimately leads to inactivation of the virus. (see Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses). UVC radiation may also be effective in inactivating the SARS-CoV-2 virus, which is the virus that causes the Coronavirus Disease 2019 (COVID-19). For more information see 'Q: Where can I read more about UV radiation and disinfection?'. However, currently there is limited published data about the wavelength, dose, and duration of UVC radiation required to inactivate the SARS-CoV-2 virus.

In addition to understanding whether UVC radiation is effective at inactivating a particular virus, there are also limitations to how effective UVC radiation can be at inactivating viruses, generally.

  • Direct exposure: UVC radiation can only inactivate a virus if the virus is directly exposed to the radiation. Therefore, the inactivation of viruses on surfaces may not be effective due to blocking of the UV radiation by soil, such as dust, or other contaminants such as bodily fluids.
  • Dose and duration: Many of the UVC lamps sold for home use are of low dose, so it may take longer exposure to a given surface area to potentially provide effective inactivation of a bacteria or virus.

UVC radiation is commonly used inside air ducts to disinfect the air. This is the safest way to employ UVC radiation because direct UVC exposure to human skin or eyes may cause injuries, and installation of UVC within an air duct is less likely to cause exposure to skin and eyes.

There have been reports of skin and eye burns resulting from improper installation of UVC lamps in rooms that humans can occupy.

Q: Can UVB or UVA radiation inactivate the SARS-CoV-2 coronavirus?

A: UVB and UVA radiation is expected to be less effective than UVC radiation at inactivating the SARS-CoV-2 coronavirus.

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  • UVB: There is some evidence that UVB radiation is effective at inactivating other SARS viruses (not SARS-CoV-2). However, it is less effective than UVC at doing so and is more hazardous to humans than UVC radiation because UVB radiation can penetrate deeper into the skin and eye. UVB is known to cause DNA damage and is a risk factor in developing skin cancer and cataracts.
  • UVA: UVA radiation is less hazardous than UVB radiation but is also significantly (approximately 1000 times) less effective than either UVB or UVC radiation at inactivating other SARS viruses. UVA is also implicated in skin aging and risk of skin cancer.

Q: Is it safe to use a UVC lamp for disinfection purposes at home?

A: Consider both the risks of UVC lamps to people and objects and the risk of incomplete inactivation of virus.

Risks: UVC lamps used for disinfection purposes may pose potential health and safety risks depending on the UVC wavelength, dose, and duration of radiation exposure. The risk may increase if the unit is not installed properly or used by untrained individuals.

  • Direct exposure of skin and eyes to UVC radiation from some UVC lamps may cause painful eye injury and burn-like skin reactions. Never look directly at a UVC lamp source, even briefly. If you have experienced an injury associated with using a UVC lamp, we encourage you to report it to the FDA.
  • Some UVC lamps generate ozone. Ozone inhalation can be irritating to the airway.
  • UVC can degrade certain materials, such as plastic, polymers, and dyed textile.
  • Some UVC lamps contain mercury. Because mercury is toxic even in small amounts, extreme caution is needed in cleaning a lamp that has broken and in disposing of the lamp.

Effectiveness: The effectiveness of UVC lamps in inactivating the SARS-CoV-2 virus is unknown because there is limited published data about the wavelength, dose, and duration of UVC radiation required to inactivate the SARS-CoV-2 virus. It is important to recognize that, generally, UVC cannot inactivate a virus or bacterium if it is not directly exposed to UVC. In other words, the virus or bacterium will not be inactivated if it is covered by dust or soil, embedded in porous surface or on the underside of a surface.

To learn more about a specific UVC lamp, you may want to:

  • Ask the manufacturer about the product’s health and safety risks and about the availability of instructions for use/training information.
  • Ask whether the product generates ozone.
  • Ask what kind of material is compatible with UVC disinfection.
  • Ask whether the lamp contains mercury. This information may be helpful if the lamp is damaged and you need to know how to clean up and/or dispose of the lamp.

Q: Are all lamps that produce UVC radiation the same?

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Not all UVC lamps are the same. Lamps may emit very specific UVC wavelengths (like 254 nm or 222 nm), or they may emit a broad range of UV wavelengths. Some lamps also emit visible and infrared radiation. The wavelengths emitted by the lamp may affect the lamp’s effectiveness at inactivating a virus and may impact the health and safety risks associated with the lamp. Some lamps emit multiple types of wavelengths. Testing of the lamp can determine whether, and how much, other wavelengths the lamp puts out.

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There is some evidence that excimer lamps, with peak wavelength of 222-nm may cause less damage to the skin, eyes, and DNA than the 254 nm wavelength, but long-term safety data is lacking. For more information see 'Q: Where can I read more about UV radiation and disinfection?'.

Q: What are the different types of lamps that can produce UVC radiation?

Low-pressure mercury lamp: Historically, the most common type of lamp used to produce UVC radiation was the low-pressure mercury lamp, which has its main (>90%) emission at 254 nm. Other wavelengths are also produced by this type of lamp. There are other lamps available that emit a broad range of UV wavelengths, but also emit visible and infrared radiation.

Excimer lamp or Far-UVC lamp: Type of lamp, called an “excimer lamp”, with a peak emission of around 222 nm.

Pulsed xenon lamps: These lamps, which emit a short pulse of broad spectrum (including UV, visible and infrared) light have been filtered to emit mainly UVC radiation and are sometimes employed in hospital settings to treat environmental surfaces in operating rooms or other spaces. These are normally employed when no humans are occupying the space.

Light-emitting diodes (LEDs): Light-emitting diodes (LEDs) that produce UV radiation are also becoming more commonly available. Typically, LEDs emit a very narrow wavelength band of radiation. Currently available UV LEDs have peak wavelengths at 265 nm, 273 nm, and 280 nm, among others. One advantage of LEDs over low-pressure mercury lamps is that they contain no mercury. However, the small surface area and higher directionality of LEDs may make them less effective for germicidal applications.

Q: Where can I read more about UV radiation and disinfection?

A: For general information about UV radiation, see Ultraviolet (UV) Radiation.

For more technical details, see these reports and publications:

  • Ultraviolet Air Disinfection (International Commission on Illumination: CIE 155:2003)
  • Germicidal Ultraviolet (GUV) – Frequently Asked Questions (Illuminating Engineering Society Committee Report: IES CR-2-20-V1)
  • Germicidal Efficacy and Mammalian Skin Safety of 222-nm UV Light (Radiation Research: 187(4); 483–491)
  • UVC Lamps and SARS-COV-2 (International Commission on Non-Ionizing Radiation Protection: ICNIRP)
  • The effect of 222-nm UVC phototesting on healthy volunteer skin: a pilot study (Photodermatology Photoimmunology Photomedicine: 31; 159–166)
  • Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses (Scientific Reports: 10; 10285)

For questions about this page, contact 1-888-INFO-FDA or the Office of Health Technology 7: Office of In Vitro Diagnostics and Radiological Health (OIR)/Division of Radiological Health (DRH) at RadHealth@fda.hhs.gov.

FDA Regulation of UVC Lamps

Q: What is the FDA’s role in the oversight of UVC lamps?

A: UVC lamps are electronic products. The FDA regulates electronic products that emit radiation (both non-medical and medical products) through the Electronic Product Radiation Control Provisions, which were originally enacted as the Radiation Control for Health and Safety Act. Certain electronic products may also be regulated as medical devices. The FDA is responsible for regulating firms who manufacture, repackage, relabel, and/or import medical devices sold in the United States.

UVC lamp manufacturers are responsible for compliance with all applicable regulatory requirements, including Title 21 Code of Federal Regulations (CFR) Parts 1000 through 1004, and section 1005.25 and, as applicable, 21 CFR Chapter I, Subchapter H. The radiological health regulations include reporting of Accidental Radiation Occurrences, notification to the FDA and customers of radiation safety defects, and designation of a U.S. agent for imported lamps. When a UVC lamp is regulated only as an electronic product, there are currently no specific FDA performance standards that apply.

Ultraviolet lamps intended for medical purposes, such as products that disinfect other medical devices or irradiate part of the human body, that meet the definition of medical device under section 201(h) of the Federal Food, Drug, and Cosmetic Act also typically require FDA clearance, approval, or authorization prior to marketing.

For further information, please see FDA’s pages, 'How to Determine if your Product is a Medical Device' and 'Overview of Device Regulation.'

UVC radiation can cause severe burns (of the skin) and eye injuries (photokeratitis). Avoid direct skin exposure to UVC radiation and never look directly into a UVC light source, even briefly. If customers identify a problem with a UVC lamp, they can report it to the manufacturer and the FDA.

Consumers who are interested in learning more about the Environmental Protection Agency’s (EPA’s) role, may want to see EPA’s page, Why aren’t ozone generators, UV lights or air purifiers on List N? Can I use them to kill the COVID-19?

As always, a function is a module of code that takes information in (referring to that information with local symbolic names called parameters), does some computation, and (usually) returns a new piece of information based on the parameter information.

Basic Function Design Pattern

For the basic syntax of a function in C, please refer to the C Function Design Pattern chapter.

Dot C files

The 'recipe' for a function (the function's code) is always stored in a '.C' file. In C there can be many functions written in a single file.

Ordering of functions in a file

The order of functions inside a file is arbitrary. It does not matter if you put function one at the top of the file and function two at the bottom, or vice versa.

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Caveat: In order for one function to 'see' (use) another function, the 'prototype' of the function must be seen in the file before the usage. If a function uses another function that is textually written above it in the file, then this will automatically be true. If the function uses a function that is 'below it' in a file, then the prototype should occur at the top of the file... see prototypes below.

A Function Prototype

In C, all functions must be written to return a specific TYPE of information and to take in specific types of data (parameters). This information is communicated to the compiler via a function prototype.

Here is the syntax for the function declaration or Prototype:

A Prototype can occur at the top of a C source code file to describe what the function returns and what it takes (return type and parameter list). When this is the case (occuring at the top of the file), the function prototype should be followed by a semi-colon

The function prototype is also used at the beginning of the code for the function. Thus the prototype can occur twice in a C source code file. When the prototype occurs with the code NO semicolon is used.

The Main Function

In C, the 'main' function is treated the same as every function, it has a return type (and in some cases accepts inputs via parameters). The only difference is that the main function is 'called' by the operating system when the user runs the program. Thus the main function is always the first code executed when a program starts.

Examples of C Functions:

Return Type of a C function

Every C function must specify the type of data that is being generated. For example, the max function above returns a value of type 'double'. Inside the function, the line 'return X;' must be found, where X is a value or variable containing a value of the given type.

The return statement

When a line of code in a function that says: 'return X;' is executed, the function 'ends' and no more code in the function is executed. The value of X (or the value in the variable represented by X) becomes the result of the function.

Calling a C function (aka invoke a function)

When one piece of code invokes or calls a function, it is done by the following syntax:

The function name must match exactly the name of the function in the function prototype. The args are a list of values (or variables containing values) that are 'passed' into the function.

The number of args 'passed' into a function must exactly match the number of parameters required for the function. The type of each arg must exactly match the type of each parameter. The return variable type must exactly match the return type of the function.

The 'variable' in the example above must have a type equivalent to the return type of the function. Inside the function, somewhere will be the line 'return X'. The value of X is then copied into the 'variable'.

Parameters in C functions

A Parameter is the symbolic name for 'data' that goes into a function. There are two ways to pass parameters in C: Pass by Value, Pass by Reference.

  • Pass by Value

    Pass by Value, means that a copy of the data is made and stored by way of the name of the parameter. Any changes to the parameter have NO affect on data in the calling function.

  • Pass by Reference

    A reference parameter 'refers' to the original data in the calling function. Thus any changes made to the parameter are ALSO MADE TO THE ORIGINAL variable.

    There are two ways to make a pass by reference parameter:

    1. ARRAYS

      Arrays are always pass by reference in C. Any change made to the parameter containing the array will change the value of the original array.

    2. The ampersand used in the function prototype.

      function ( & parameter_name )

      To make a normal parameter into a pass by reference parameter, we use the '& param' notation. The ampersand (&) is the syntax to tell C that any changes made to the parameter also modify the original variable containing the data.

Pass by Value Example:

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In C, the default is to pass by value. For example:

Pass by Reference Example:

Warning: C++

I suggest that you use a C++ compiler such as g++ which allows the following pass by reference syntax (a much more modern style). The Syntax is to use the '&' in front of the parameter name in the function declaration. The calling code and usage inside the function are the same as before. For example:

Warning: Standard C - Using 'Pointers'

With standard C you have to put the & in the calling location as opposed to next to the parameter in the function declaration; further, you must use a '*' in the parameter list, and use a '*' whenever using the parameter inside the function.

The '*' is used to define a 'pointer', a discussion of which is beyond the scope of this simple example. Feel free to Google 'Pointers in C' for a long treatise on how to use them... or take my advice, and (as a beginning programmer) avoid them.

In summary, if you use a reference parameter, any changes to the parameter inside the function are reflected 'outside' of the function (i.e., in the calling function)! If you don't use the & (pass by reference), then we get the same behavior as in Matlab (i.e., the value is changed inside the called function, but maintains its original value in the calling function.

One reason to use reference parameters is to make the program more 'efficient'. Consider passing in a structure as a parameter. If the structure is very big, and we copy all of it, then we are using a lot of unnecessary memory.

Array Parameter Example (ALWAYS pass by reference)

Arrays are always passed by reference in C. They do not use the '&' notation, but are pass by reference none the less. For example:

Constant Reference

To protect from accidentally changing a reference parameter, when we really want it not to be changed (we just want to save time/memory) we can use the C keyword const. For example:

Void Functions

If a function does not return a value, then a special 'TYPE' is used to tell the computer this. The return type is 'void' (all lower case).

Void functions are mostly used in two classes of functions.

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  1. The first is a function that prints information for the user to read. For example (for our purposes), the printf function is treated as a void function. (In actuality, printf returns an integer which is the number of characters printed... but we almost always ignore this value.)

  2. The second use of void functions is with 'reference' parameters (e.g., Arrays). A reference parameter is not a copy of the input data, as is so often the case. A reference parameter is an 'alias' for the same bucket in memory as the input data. Thus any change made to a reference parameter is in fact made to the original variable!