我正在尝试将GSL GNU库集成到我的iPhone应用程序中。我将所有文件复制到我的Xcode项目中，但它们给了我错误。我不知道为什么会出现这个错误。
请帮我解决这个问题。
错误记录
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find2d.c:20:10: In file included from /Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find2d.c:20:
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:24:34: Unknown type name 'size_t'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:27:13: Unknown type name 'size_t'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:27:61: Unknown type name 'size_t'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:29:3: Use of undeclared identifier 'size_t'; did you mean 'sizeof'?
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:29:10: Use of undeclared identifier 'i_linear'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:29:20: Use of undeclared identifier 'lower'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:29:27: Use of undeclared identifier 'upper'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:29:34: Use of undeclared identifier 'mid'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:46:5: Use of undeclared identifier 'i_linear'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:46:17: Use of undeclared identifier 'size_t'; did you mean 'sizeof'?
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:49:18: Use of undeclared identifier 'i_linear'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:49:41: Use of undeclared identifier 'i_linear'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:51:12: Use of undeclared identifier 'i_linear'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:58:3: Use of undeclared identifier 'upper'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:59:3: Use of undeclared identifier 'lower'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:61:10: Use of undeclared identifier 'upper'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:61:18: Use of undeclared identifier 'lower'
/Users/manas/Desktop/DerivativeApp/gsl-1.9 2/histogram/find.c:63:7: Use of undeclared identifier 'mid'
Too many errors emitted, stopping now.