"exif.c" is a simple implementation to access the Exif segment in a JPEG file.
It easily enables you to get the value of the IFD tag field with such code:

  TagNodeInfo *tag = getTagInfo(ifdArray, IFD_EXIF, TAG_DateTimeOriginal);
  printf("DateTimeOriginal = [%s]\n", tag->byteData);

  -> DateTimeOriginal = [2013:09:01 09:49:00]

See "sample_main.c" and "exif.h" for details.

exif.c only uses standard C library functions. So, it will be usable in many environments. 
It has been tested in the following environments.

 - Windows XP 32bit + 32bit Visual C++
 - Windows 7 64bit + 64bit Visual C++
 - Redhat Linux 32bit + 32bit gcc
 - Mac OS X 64bit + 64bit gcc

building with gcc:
gcc -o exif sample_main.c exif.c

building with Microsoft Visual C++:
cl.exe /o exif sample_main.c exif.c

The following output is the result of the sample program.
---------------------------------------------------------------------------
$ exif test.jpg

[test.jpg] createIfdTableArray: result=4

{0TH IFD}
 - Make: [Apple]
 - Model: [iPod touch]
 - Orientation: 1
 - XResolution: 72/1
 - YResolution: 72/1
 - ResolutionUnit: 2
 - Software: [6.1.4]
 - DateTime: [2013:09:01 09:49:00]
 - YCbCrPositioning: 1
 - ExifIFDPointer: 206
 - GPSInfoIFDPointer: 576

{EXIF IFD}
 - ExposureTime: 1/30
 - FNumber: 12/5
 - ExposureProgram: 2
 - PhotographicSensitivity: 400
 - ExifVersion: 0 2 2 1
 - DateTimeOriginal: [2013:09:01 09:49:00]
 - DateTimeDigitized: [2013:09:01 09:49:00]
 - ComponentsConfiguration: 0x01 0x02 0x03 0x00
 - ShutterSpeedValue: 4035/821
 - ApertureValue: 4845/1918
 - BrightnessValue: 2234/1113
 - MeteringMode: 5
 - Flash: 32
 - FocalLength: 77/20
 - FlashPixVersion: 0 1 0 0
 - ColorSpace: 1
 - PixelXDimension: 960
 - PixelYDimension: 720
 - SensingMethod: 2
 - ExposureMode: 0
 - WhiteBalance: 0
 - FocalLengthIn35mmFormat: 32
 - SceneCaptureType: 0

{GPS IFD}
 - GPSLatitudeRef: [S]
 - GPSLatitude: 69/1 17/100 0/1
 - GPSLongitudeRef: [E]
 - GPSLongitude: 39/1 35/100 0/1
 - GPSAltitudeRef: 0
 - GPSAltitude: 6151/470
 - GPSTimeStamp: 0/1 48/1 3921/100

{1ST IFD}
 - Compression: 6
 - XResolution: 72/1
 - YResolution: 72/1
 - ResolutionUnit: 2
 - JPEGInterchangeFormat: 840
 - JPEGInterchangeFormatLength: 8648

0th IFD : Model = [iPod touch]
Exif IFD : DateTimeOriginal = [2013:09:01 09:49:00]
GPS IFD : GPSLatitude = 69/1 17/100 0/1
removeExifSegmentFromJPEGFile: result=1
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