Getting tons of errors when compiling a C program

Question

I was trying to run the following program when this big error occurred. What am I doing wrong?

#include <stdio.h> #include <fcntl.h> #include <unistd.h> #include <string.h> #include <stdlib.h> int main() { char *file = "zahl.txt"; int fd; struct flock lock = { F_WRLCK, SEEK_SET, 0, 0, 0 }; lock.l_pid = getpid(); fd = open(file, O_RDWR | O_APPEND); if (fcntl(fd, F_SETLKW, &lock) != -1) //setting the lock to wait while another instance is already running { FILE *fp1; int i; char buff[255]; fp1 = fopen(file, "a+"); //read from file while (fgets(buff, 255, fp1) != NULL); //moves to last line of file i = atoi(buff); i++; char temp[10]; sprintf(temp, "%d\n", i); //printing the incremented value to temp fputs(temp, fp1); fclose(fp1); lock.l_type = F_UNLCK; fcntl(fd, F_SETLK, &lock); close(fd); } return 0; }

 [rmig0489@linux Assign9]$ gcc -Wall -o -g ink ink.c 
ink: In function _start': (.text+0x0): multiple definition of _start' /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../lib64/crt1.o:(.text+0x0): first defined here ink: In function _fini': (.fini+0x0): multiple definition of _fini' /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../lib64/crti.o:(.fini+0x0): first defined here ink:(.rodata+0x0): multiple definition of _IO_stdin_used' /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../lib64/crt1.o:(.rodata.cst4+0x0): first defined here ink: In function __data_start': (.data+0x0): multiple definition of __data_start' /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../lib64/crt1.o:(.data+0x0): first defined here ink:(.rodata+0x8): multiple definition of __dso_handle' /usr/lib/gcc/x86_64-redhat-linux/4.4.7/crtbegin.o:(.rodata+0x0): first defined here ink: In function _init': (.init+0x0): multiple definition of _init' /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../lib64/crti.o:(.init+0x0): first defined here /tmp/ccmuhndv.o: In function main': ink.c:(.text+0x0): multiple definition of main' ink:/home/scs/licenta/an1/gr712/rmig0489/C-Programm/Assign9/ink.c:6: first defined here /usr/lib/gcc/x86_64-redhat-linux/4.4.7/crtend.o:(.dtors+0x0): multiple definition of `DTOR_END' ink:(.dtors+0x8): first defined here /usr/bin/ld: warning: Cannot create .eh_frame_hdr section, --eh-frame-hdr ignored. /usr/bin/ld: error in ink(.eh_frame); no .eh_frame_hdr table will be created. collect2: ld returned 1 exit status

For all options that require a parameter, that parameter must follow immediately after the option. Your command tellS gcc to use filename -g as output file and ink ink.c as input files. — Gerhardh
– Gerhardh, Commented May 29, 2022 at 11:01

chqrlie · Accepted Answer · 2022-05-29 11:39:49Z

The problem is in the command line: gcc -Wall -o -g ink ink.c

The -o argument must be followed by the name of the output file, so -g is used for that, and gcc sees ink (the executable produced by a previous command) as a binary module to link along with the object module compiled from ink.c and the C library, hence all the duplicate internal symbols.

Use this command:

gcc -Wall -g -o ink ink.c

Note also these problems in your code:

relying on the contents of buff after the last call to fgets() is incorrect, especially if the file happens to be empty. You should instead convert each and every line successfully read and use the last conversion.
you must call fseek(fp1, 0L, SEEK_CUR) before switching from reading the file to writing to it.
char temp[10]; is not large enough to convert all possible int values. You should make the array larger and use snprintf for safety.

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