How to read image file and allocate memory using malloc?

skyjuice (3)
I am new to compiling in linux environment. Anyway, I have a source code in C which is suppose to read a sequence of .pgm image files, compress them and write the compressed file to a new .pgm file. However, when I compile I get the following error message

*** glibc detected *** ./a.out: free(): invalid pointer: 0x00007fefc6176010 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x7a6e6)[0x7fefda73b6e6]
/lib/x86_64-linux-gnu/libc.so.6(cfree+0x6c)[0x7fefda73f9cc]
./a.out[0x408491]
./a.out[0x408565]
./a.out[0x401048]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed)[0x7fefda6e230d]
./a.out[0x400a59]
======= Memory map: ========
00400000-0040b000 r-xp 00000000 07:00 299109 /home/skyjuice/PROJECT3/a.out
0060a000-0060b000 r--p 0000a000 07:00 299109 /home/skyjuice/PROJECT3/a.out
0060b000-0060c000 rw-p 0000b000 07:00 299109 /home/skyjuice/PROJECT3/a.out
0060c000-059f8000 rw-p 00000000 00:00 0
05ebb000-05ee3000 rw-p 00000000 00:00 0 [heap]
7fefc0000000-7fefc0021000 rw-p 00000000 00:00 0
7fefc0021000-7fefc4000000 ---p 00000000 00:00 0
7fefc59d3000-7fefc59d4000 rw-p 00000000 00:00 0
7fefc5f60000-7fefc5f75000 r-xp 00000000 07:00 2117 /lib/x86_64-linux-gnu/libgcc_s.so.1
7fefc5f75000-7fefc6174000 ---p 00015000 07:00 2117 /lib/x86_64-linux-gnu/libgcc_s.so.1
7fefc6174000-7fefc6175000 r--p 00014000 07:00 2117 /lib/x86_64-linux-gnu/libgcc_s.so.1
7fefc6175000-7fefc6176000 rw-p 00015000 07:00 2117 /lib/x86_64-linux-gnu/libgcc_s.so.1
7fefc6176000-7fefda6c1000 rw-p 00000000 00:00 0
7fefda6c1000-7fefda858000 r-xp 00000000 07:00 904195 /lib/x86_64-linux-gnu/libc-2.13.so
7fefda858000-7fefdaa57000 ---p 00197000 07:00 904195 /lib/x86_64-linux-gnu/libc-2.13.so
7fefdaa57000-7fefdaa5b000 r--p 00196000 07:00 904195 /lib/x86_64-linux-gnu/libc-2.13.so
7fefdaa5b000-7fefdaa5c000 rw-p 0019a000 07:00 904195 /lib/x86_64-linux-gnu/libc-2.13.so
7fefdaa5c000-7fefdaa62000 rw-p 00000000 00:00 0
7fefdaa62000-7fefdaae5000 r-xp 00000000 07:00 904199 /lib/x86_64-linux-gnu/libm-2.13.so
7fefdaae5000-7fefdace4000 ---p 00083000 07:00 904199 /lib/x86_64-linux-gnu/libm-2.13.so
7fefdace4000-7fefdace5000 r--p 00082000 07:00 904199 /lib/x86_64-linux-gnu/libm-2.13.so
7fefdace5000-7fefdace6000 rw-p 00083000 07:00 904199 /lib/x86_64-linux-gnu/libm-2.13.so
7fefdace6000-7fefdad07000 r-xp 00000000 07:00 644102 /lib/x86_64-linux-gnu/ld-2.13.so
7fefdaeeb000-7fefdaeee000 rw-p 00000000 00:00 0
7fefdaf04000-7fefdaf06000 rw-p 00000000 00:00 0
7fefdaf06000-7fefdaf07000 r--p 00020000 07:00 644102 /lib/x86_64-linux-gnu/ld-2.13.so
7fefdaf07000-7fefdaf09000 rw-p 00021000 07:00 644102 /lib/x86_64-linux-gnu/ld-2.13.so
7fff1b020000-7fff1b0ca000 rw-p 00000000 00:00 0 [stack]
7fff1b148000-7fff1b149000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
Aborted


Below is a snippet of the source code

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#define START_FRAME 141
    #define END_FRAME 143
    #define SKIP_FRAME 1
    #define INPUT_STRING "/home/image%03d.pgm"
    
    int main(int argv, char *argc[])
    {
    
      unsigned char *frm1, *frm2, *predict, *predictDb, *frm1E;    
      unsigned char *rcnDiff, *diff, *rcnFrm1, *rcnFrm2, *wave;  
      int           *xVct, *yVct, *pxE, *pyE, *code;  
      int   nx  = 1920, ny = 1080, nxy;  
      int   bSize  = 16, nbx, nby, nbxy;
    
      frm1       = (unsigned char *) malloc(sizeof(unsigned char) * nxy);  
      frm2       = (unsigned char *) malloc(sizeof(unsigned char) * nxy);  
      rcnFrm1    = (unsigned char *) malloc(sizeof(unsigned char) * nxy);  
      rcnFrm2    = (unsigned char *) malloc(sizeof(unsigned char) * nxy);  
      predict    = (unsigned char *) malloc(sizeof(unsigned char) * nxy);  
      predictDb  = (unsigned char *) malloc(sizeof(unsigned char) * nxy);  
      diff       = (unsigned char *) malloc(sizeof(unsigned char) * nxy);  
      rcnDiff    = (unsigned char *) malloc(sizeof(unsigned char) * nxy);  
      wave       = (unsigned char *) malloc(sizeof(unsigned char) * nxy);    
      xVct       = (int *) malloc(sizeof(int) * nbxy);  
      yVct       = (int *) malloc(sizeof(int) * nbxy);  
      
      code       = (int *) malloc(sizeof(int) * tgtBits1);    
      frm1d      = (double *) malloc(sizeof(double) * nxy);  
      frm2d      = (double *) malloc(sizeof(double) * nxy);  
      predictd   = (double *) malloc(sizeof(double) * nxy);  
      predictDbd = (double *) malloc(sizeof(double) * nxy);  
      rcnFrm1d   = (double *) malloc(sizeof(double) * nxy);  
      rcnFrm2d   = (double *) malloc(sizeof(double) * nxy);  
      wavFrm1    = (double *) malloc(sizeof(double) * nxy);  
      wavDiff    = (double *) malloc(sizeof(double) * nxy);  
      wavRcnFrm1 = (double *) malloc(sizeof(double) * nxy);  
      wavRcnDiff = (double *) malloc(sizeof(double) * nxy);  
      diffd      = (double *) malloc(sizeof(double) * nxy);  
      rcnDiffd   = (double *) malloc(sizeof(double) * nxy);  
      
      frm1Ed     = (double *) malloc(sizeof(double) * nxE * nyE);  
      frm1E      = (unsigned char *) malloc(sizeof(unsigned char) * nxE * nyE);
    
      //read file from PGM and store into frm1  
      frameNo = START_FRAME;  
      sprintf(fileName, INPUT_STRING, frameNo);  
      readPgm(frm1, fileName, nx, ny);  
      
      //after some operations
    
      //write into a new PGM file  
       sprintf(fileName, "predictDb%03d.pgm", frameNo);  
       writePgm(predictDb, fileName, nx, ny);  
    
      return 0; //end of main function   
    }  
    
    //read original frame  
    void readPgm(unsigned char *frame, char * fileName, int nx, int ny) {  
      int i, j;  
      FILE *file;  
      char str[128];  
    
      file = fopen(fileName,"r");  
      if (file == 0) {  
        printf("Open error in File read \n");  
          }  
      fgets(str, 100, file);  
      for(j = 0; j < ny; j++) {  
          for(i = 0; i < nx; i++) {  
    	fscanf(file,"%d", (int *)&frame[i + nx * j]);  
          }  
      }  
      fclose(file);  
    }  
    
    
    //create frame  
    void writePgm(unsigned char *frame, char *fileName, int nx, int ny){  
      int i, j;  
      FILE *file;  
    
      file = fopen(fileName, "w");  
      fprintf(file, "P2 %d %d 255\n", nx, ny);  
      for(j = 0; j < ny; j++) {  
        for(i = 0; i < nx; i++) {  
          fprintf(file,"%d ", frame[i + nx * j]);  
        }  
        fprintf(file, "\n");  
      }  
      fclose(file);  
    }


Can anyone help identify what the problem is? Thank you
Ben Brown (25)
Remember that sizeof() returns the number of bytes that the variable, array, or whatever takes up. So instead of returning the value of a variable, it returns the number of bytes the variable takes up. I'm not really sure if that will make a difference at all, because I'm new to C++ and have never programmed in C before (and am pretty confused by your code), so I could be completely wrong. Let me know if this helps, or if you find the answer.
Last edited on
kbw (9488)
nxy is used to determine the size of the allocated blocks, but is itself uninitialised.
skyjuice (3)
Sorry, I actually did initialize nyz but did not include it in my code above. So I guess the problem is not due to this. Anymore possible causes?
b2ee (74)
Did the error happen exactly in compiling? It's more like in running.
skyjuice (3)
Anyway, when I change the line to
 
 
fscanf(file,"%c", &frame[i + nx * j]);
There is no warning during compiling but now I encounter this warning during running.

*** glibc detected *** ./a.out: double free or corruption (out): 0x00007f91023df010 ***

Is this due to malloc where too much memory is allocated?

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