I use uVision3 V3.30a Philips LPC2294. When I run program with File Handle I can't link it. Such as I use fopen , fclose , fpprintf , f... ,when I build program it has errors. This is my program. #include <ARTX.h> #include <LPC22xx.H> #include <stdio.h> #include <ARTX_Config.h> void init_serial(void){ /* initialize the serial interface */ PINSEL0 = 0x00050005; /* Enable RxD1 and TxD1 */ U0LCR = 0x83; /* 8 bits, no Parity, 1 Stop bit */ U0DLL = 97; /* 9600 Baud Rate @ 15MHz VPB Clock */ U0LCR = 0x03; /* DLAB = 0 */ } unsigned char mempool[0x100000]; int main(void) { FILE *out; init_mempool(mempool,sizeof(mempool)); init_serial(); if(!(out=fopen("testfile.txt","r"))) { printf("Error: Cannot open output file!\n"); return 1; } fclose(out); return 0; } In the Linking time ,it show me the errors... *** WARNING L23: UNRESOLVED EXTERNAL SYMBOLS *** ERROR L128: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: fopen?T ADDRESS: 00000222H *** ERROR L128: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: fclose?T ADDRESS: 0000023EH I can't run it although i include ARTX.h