valgrind

I try to profile a simple c prog using valgrind: [zsun@nel6005001 ~]$ valgrind --tool=memcheck ./fl.out ==2238== Memcheck, a memory error detector ==2238== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al. ==2238== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info ==2238== Command: ./fl.out ==2238== ==2238== ==2238== HEAP SUMMARY: ==2238== in use at exit: 1,168 bytes in 1 blocks ==2238== total heap usage: 1 allocs, 0 frees, 1,168 bytes allocated ==2238== ==2238== LEAK SUMMARY: ==2238== definitely lost: 0 bytes in 0 blocks ==2238== indirectly lost: 0 bytes in 0

I've been debugging some app lately with valgrind, and I'm getting very weird reports from dlopen . ==1987== 32 bytes in 1 blocks are still reachable in loss record 1 of 2 ==1987== at 0x4C24477: calloc (vg_replace_malloc.c:418) ==1987== by 0x570F31F: _dlerror_run (dlerror.c:142) ==1987== by 0x570EEE0: dlopen@@GLIBC_2.2.5 (dlopen.c:88) <my call to dlopen> ==1987== ==1987== 264 bytes in 1 blocks are still reachable in loss record 2 of 2 ==1987== at 0x4C25153: malloc (vg_replace_malloc.c:195) ==1987== by 0x400CD44: _dl_map_object_deps (dl-deps.c:506) ==1987== by 0x4012DA2: dl_open_worker (dl-open

I'm corrupting memory somehow because my program crashes without error at random places. I'm using valgrind with --leak-check=full , compiling with -O0 -g , and the very first problem it detects is the first line in int main() cout << "reading file" << endl; with ==5089== Warning: client switching stacks? SP change: 0x7ff0004f8 --> 0x7feb7de10 ==5089== to suppress, use: --max-stackframe=4728552 or greater ==5089== Invalid write of size 8 ==5089== at 0x41E107: main (Dgn.cpp:2833) ==5089== Address 0x7feb7de08 is on thread 1's stack It goes on with ==5089== Invalid read of size 8 ==5089== at

This question already has an answer here: Facing an error “*** glibc detected *** free(): invalid next size (fast)” 2 answers The code below breaks on the fclose() call. void output_gauss_transform(char* filename, char* mode, double** T, double shift, int len) { FILE* fp; printf("Outputting gauss transform to %s.\n", filename); if ((fp = fopen(filename, mode)) == NULL){ perror("Could not open file"); return; } int i; for (i = 0; i < len; ++i) { fprintf(fp, "%lf %lf\n", T[0][i], T[1][i] + shift); } if (fclose(fp)){ printf("error closing\n"); } } glibc gives me this error, along with the memory