first time poster here.
I'm trying to write a block of code in c that takes a struct with 5 different strings (each a max of 32 characters) that concatenates the whole lot into a single comma-separated string and writes it to a text file. I've done a similar thing using c++ and it's worked fine, the problem I'm having with my c version is, I think, in this part of the code...

char *out[256] = {(char*)malloc(sizeof(*out))}; int i; *out = conc(v); printf("%s\n", *out); FILE *fp; fp = fopen(fname, "w"); i = fprintf(fp, *out); printf("i = %d\n", i); fclose(fp); I believe the problem is in the i = fprintf(fp, *out) line, whenever the total character count of out is over 25 characters the program crashes and dumps the following to the console...

*** glibc detected *** ./file2: free(): invalid next size (normal): 0x00000000011d5100 *** ======= Backtrace: ========= /lib/x86_64-linux-gnu/libc.so.6(+0x76d76)[0x7f62635f4d76] /lib/x86_64-linux-gnu/libc.so.6(cfree+0x6c)[0x7f62635f9aac] /lib/x86_64-linux-gnu/libc.so.6(fclose+0x14d)[0x7f62635e5ccd] ./file2[0x400f08] ./file2[0x400a95] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xfd)[0x7f626359cead] ./file2[0x400969] ======= Memory map: ======== 00400000-00402000 r-xp 00000000 08:01 2099569 /home/richard/Documents/C/file2 00601000-00602000 rw-p 00001000 08:01 2099569 /home/richard/Documents/C/file2 011d5000-011f6000 rw-p 00000000 00:00 0 [heap] 7f625c000000-7f625c021000 rw-p 00000000 00:00 0 7f625c021000-7f6260000000 ---p 00000000 00:00 0 7f626357e000-7f62636fe000 r-xp 00000000 08:01 2883603 /lib/x86_64-linux-gnu/libc-2.13.so 7f62636fe000-7f62638fe000 ---p 00180000 08:01 2883603 /lib/x86_64-linux-gnu/libc-2.13.so 7f62638fe000-7f6263902000 r--p 00180000 08:01 2883603 /lib/x86_64-linux-gnu/libc-2.13.so 7f6263902000-7f6263903000 rw-p 00184000 08:01 2883603 /lib/x86_64-linux-gnu/libc-2.13.so 7f6263903000-7f6263908000 rw-p 00000000 00:00 0 7f6263908000-7f626391d000 r-xp 00000000 08:01 2883588 /lib/x86_64-linux-gnu/libgcc_s.so.1 7f626391d000-7f6263b1d000 ---p 00015000 08:01 2883588 /lib/x86_64-linux-gnu/libgcc_s.so.1 7f6263b1d000-7f6263b1e000 rw-p 00015000 08:01 2883588 /lib/x86_64-linux-gnu/libgcc_s.so.1 7f6263b1e000-7f6263b9f000 r-xp 00000000 08:01 2883600 /lib/x86_64-linux-gnu/libm-2.13.so 7f6263b9f000-7f6263d9e000 ---p 00081000 08:01 2883600 /lib/x86_64-linux-gnu/libm-2.13.so 7f6263d9e000-7f6263d9f000 r--p 00080000 08:01 2883600 /lib/x86_64-linux-gnu/libm-2.13.so 7f6263d9f000-7f6263da0000 rw-p 00081000 08:01 2883600 /lib/x86_64-linux-gnu/libm-2.13.so 7f6263da0000-7f6263e88000 r-xp 00000000 08:01 266029 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.17 7f6263e88000-7f6264088000 ---p 000e8000 08:01 266029 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.17 7f6264088000-7f6264090000 r--p 000e8000 08:01 266029 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.17 7f6264090000-7f6264092000 rw-p 000f0000 08:01 266029 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.17 7f6264092000-7f62640a7000 rw-p 00000000 00:00 0 7f62640a7000-7f62640c7000 r-xp 00000000 08:01 2883606 /lib/x86_64-linux-gnu/ld-2.13.so 7f62642ab000-7f62642b0000 rw-p 00000000 00:00 0 7f62642c2000-7f62642c6000 rw-p 00000000 00:00 0 7f62642c6000-7f62642c7000 r--p 0001f000 08:01 2883606 /lib/x86_64-linux-gnu/ld-2.13.so 7f62642c7000-7f62642c8000 rw-p 00020000 08:01 2883606 /lib/x86_64-linux-gnu/ld-2.13.so 7f62642c8000-7f62642c9000 rw-p 00000000 00:00 0 7fff9a5f6000-7fff9a617000 rw-p 00000000 00:00 0 [stack] 7fff9a761000-7fff9a762000 r-xp 00000000 00:00 0 [vdso] ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall] Aborted When the contents of out is less than 25 characters this works perfectly. I'm still reasonably new to c/c++ so I'm sure i'm doing something obviously stupid, just mot sure what it is.
This is running on Debian (7.3 I think, the latest version), I havent had the opportunity to try it on any other computer or OS.
I've had a bit of a poke around the internet to see if there's any way to set a buffer for fprintf, if there is I haven't been able to find it.
Thank you all for any help you may be able to give.


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