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I didn't want to reinvent the wheel, so I downloaded libtga which seemed to have a convenient and simple API. Building was easy, but I stumbled upon a weird segmentation fault I can not explain. A small example:

#include <stdio.h>
#include "tga.h"
#define TEST

int main()
{
    TGA *tga;
    TGAData data;

    tga = TGAOpen("test.tga", "r");
    if(!tga || tga->last != TGA_OK) 
    { printf("TGAOpen failed\n"); return 1; }
    if(TGAReadImage(tga, &data) != TGA_OK)
    { printf("TGAReadImage failed\n"); return 1; }
    TGAHeader *header = &tga->hdr;
    printf("image dimensions:\n width: %d\t height:%d\t depth:%d bpp\n", 
           header->width, header->height, header->depth);
    tbyte *img = data.img_data;

    if (img== NULL)
    {
        printf("Pointer wrong\n");
        return 1;            
    }
    printf("pointer: %p\n", img);

    printf("test %hhu\n", img[0]);

#ifdef TEST    
    for(int i=0; i<header->height; i++)
    {
        for(int j=0; j<header->width; j++)
        {
            int index = 4*(i*header->width + j);
            printf("%3d %3d %3d %3d | ", img[index], img[index+1], img[index+2], img[index+3]);
        }
        printf("\n");
    }
#endif
    TGAClose(tga);
    return 0;
}

I compile the program with: gcc -g --std=c99 -O0 tgatest.c -L./lib -ltga -I./include

Now, if "TEST" is defined everything works fine and the values for each pixel are printed to stdout (I use a 4x4 image). If I don't define "TEST" it throws a segmentation fault at line 

printf("test %hhu\n", img[0]);

I don't understand why. Debugging shows that "img" is "Address 0x1 out of bounds", but with "TEST" it is a valid address. Any suggestions how to further investigate this? I thought the compiler may optimize things away, but -O0 doesn't change anything. Same for the --std=c99.

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1 回答 1

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根据tgalib 文档，您需要在调用之前进行设置TGA_IMAGE_DATA，data->flags以TGAReadImage确保读取图像数据。有可能在 TEST 构建中，数据变量下堆栈上的垃圾恰好设置了该位，但在其他构建中没有。

在调用之前添加如下一行TGAReadImage应该可以解决问题：

data.flags = TGA_IMAGE_DATA;
于 2014-05-14T20:44:21.120 回答