atmel studio output i2c problem

------ Build started: Project: test_i2c, Configuration: Debug AVR ------
Build started.
Project "test_i2c.cppproj" (default targets):
Target "PreBuildEvent" skipped, due to false condition; ('$(PreBuildEvent)'!='') was evaluated as (''!='').
Target "CoreBuild" in file "E:\Programme\Atmel\Studio\7.0\Vs\Compiler.targets" from project "D:\AVR_data\test\test_i2c\test_i2c\test_i2c.cppproj" (target "Build" depends on it):
	Task "RunCompilerTask"
		Shell Utils Path E:\Programme\Atmel\Studio\7.0\shellUtils
		E:\Programme\Atmel\Studio\7.0\shellUtils\make.exe all --jobs 8 --output-sync
		Building file: .././main.cpp
		Invoking: AVR8/GNU C Compiler : 5.4.0
		"E:\Programme\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\bin\avr-g++.exe" -funsigned-char -funsigned-bitfields -DDEBUG  -I"E:\Programme\Atmel\Studio\7.0\Packs\atmel\ATtiny_DFP\1.3.229\include"  -O1 -ffunction-sections -fdata-sections -fpack-struct -fshort-enums -g2 -Wall -mmcu=attiny26 -B "E:\Programme\Atmel\Studio\7.0\Packs\atmel\ATtiny_DFP\1.3.229\gcc\dev\attiny26" -c -MD -MP -MF "main.d" -MT"main.d" -MT"main.o"   -o "main.o" ".././main.cpp"
		Finished building: .././main.cpp
		Building target: test_i2c.elf
		Invoking: AVR8/GNU Linker : 5.4.0
		"E:\Programme\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\bin\avr-g++.exe" -o test_i2c.elf  i2cmaster.o main.o   -Wl,-Map="test_i2c.map" -Wl,--start-group -Wl,-lm  -Wl,--end-group -Wl,--gc-sections -mmcu=attiny26 -B "E:\Programme\Atmel\Studio\7.0\Packs\atmel\ATtiny_DFP\1.3.229\gcc\dev\attiny26"
D:\AVR_data\test\test_i2c\test_i2c\Debug\Makefile(118,1): error: recipe for target 'test_i2c.elf' failed
		main.o: In function `main':
D:\AVR_data\test\test_i2c\test_i2c\main.cpp(5,1): error: undefined reference to `i2c_init()'
collect2.exe(0,0): error: ld returned 1 exit status
		make: *** [test_i2c.elf] Error 1
		The command exited with code 2.
	Done executing task "RunCompilerTask" -- FAILED.
Done building target "CoreBuild" in project "test_i2c.cppproj" -- FAILED.
Done building project "test_i2c.cppproj" -- FAILED.

Build FAILED.
========== Build: 0 succeeded or up-to-date, 1 failed, 0 skipped ==========