獲取圖片格式類型方法...

    根據圖片文件名和圖片文件頭標識判斷圖片格式...具體請看這篇文章：http://www.cnblogs.com/sunsoft/archive/2012/01/04/2311989.html

下面是本人本身寫的一點代碼，但願有高人路過，指點更高名的方法，謝謝。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <errno.h>

#define EFFECTIVELEN 10
#define GETBYTELEN   2

/*---JPEG/JPG(1)---*/
#define IMAGE_JPEG_JPG "JPEG/JPG"
#define JPEG_FIRSTBIT  "FF"
#define JPEG_SECONDBIT "D8"

/*---BMP(2)---*/
#define IMAGE_BMP     "BMP"
#define BMP_FIRSTBIT  "42"
#define BMP_SECONDBIT "4D"

/*---PNG(3)---*/
#define IMAGE_PNG     "PNG"
#define PNG_FIRSTBIT  "89"
#define PNG_SECONDBIT "50"

/*---GIF(4)---*/
#define IMAGE_GIF     "GIF"
#define GIF_FIRSTBIT  "47"
#define GIF_SECONDBIT "49"
#define GIF_THIRDBIT  "46"
#define GIF_FIFTHBIT1 "39"   // 可能存在是37
#define GIF_FIFTHBIT2 "37"

/*---TIFF(5)---*/
#define IMAGE_TIFF      "TIFF"
#define TIFF_FIRSTBIT   "4D"
#define TIFF_SECONDBIT  "4D"
#define TIFF_FIRSTBIT2  "49"  // 或者
#define TIFF_SECONDBIT2 "49"

/*---ICO(6)---*/
#define IMAGE_ICO    "ICO"
#define ICO_THIRDBIT "1"  // 01
#define ICO_FIFTHBIT "1"  // 01

/*---TGA(7)---*/
#define IMAGE_TGA    "TGA"
#define TGA_THIRDBIT "2"  // 02
#define TGA_FIFTHBIT "0"  // 00

/*---CUR(8)---*/
#define IMAGE_CUR    "CUR"
#define CUR_THIRDBIT "2"  // 02
#define CUR_FIFTHBIT "1"  // 01

/*---PCX(9)---*/
#define IMAGE_PCX    "PCX"
#define PCX_FIRSTBIT "A"  // 0A

/*---IFF(10)---*/
#define IMAGE_IFF     "IFF"
#define IFF_FIRSTBIT  "46"
#define IFF_SECONDBIT "4F"
#define IFF_THIRDBIT  "52"
#define IFF_FORTHBIT  "4D"

/*---ANI(11)---*/
#define IMAGE_ANI     "ANI"
#define ANI_FIRSTBIT  "52"
#define ANI_SECONDBIT "49"
#define ANI_THIRDBIT  "46"
#define ANI_FORTHBIT  "46"

char MImagesType[12][10] = {"JPEG","JPG","BMP","PNG","GIF","TIFF","aICO","TGA",
                              "CUR","PCX","IFF","ANI"};
char LImagesType[12][10] = {"jpeg","jpg","bmp","png","gif","tiff","aico","tga",
                              "cur","pcx","iff","ani"};

// 反轉字符串
void reserve(char *p, char *q)
{
     while(p < q){
          *p ^= *q;
          *q ^= *p;
          *p ^= *q;
          p++;
          q--;
     }
}

char *JudgmentImageByDate(char *Filename)
{
     FILE *fd;
     unsigned char *imagebuf;
     int filesize = 0;
     unsigned char firstBit[3];
     unsigned char secondBit[3];
     unsigned char thirdBit[3];
     unsigned char forthBit[3];
     unsigned char fifthBit[3];

     assert(Filename != NULL);

     if( (fd = fopen(Filename, "rb")) == NULL){
          perror("fopen error\n");
          exit(1);
     }

     fseek(fd, 0, SEEK_END);
     filesize = ftell(fd);               // 返回當前文件位置，也就是說返回FILE指針當前位置。
     rewind(fd);                            // 將文件內部的位置指針從新指向一個流（數據流/文件）的開頭

     imagebuf = (unsigned char *)malloc(EFFECTIVELEN * sizeof(unsigned char) + 1);
     fread(imagebuf, sizeof(unsigned char), EFFECTIVELEN, fd);

     snprintf(firstBit, sizeof(firstBit), "%X", imagebuf[0]);
     snprintf(secondBit, sizeof(secondBit), "%X", imagebuf[1]);
     snprintf(thirdBit, sizeof(thirdBit), "%X", imagebuf[2]);
     snprintf(forthBit, sizeof(forthBit), "%X", imagebuf[3]);
     snprintf(fifthBit, sizeof(fifthBit), "%X", imagebuf[4]);

     if( (0 == strncmp(firstBit, JPEG_FIRSTBIT,      GETBYTELEN)) &&
          (0 == strncmp(secondBit, JPEG_SECONDBIT, GETBYTELEN))) {
          return IMAGE_JPEG_JPG;
     }
     if( (0 == strncmp(firstBit, BMP_FIRSTBIT,      GETBYTELEN)) &&
          (0 == strncmp(secondBit, BMP_SECONDBIT, GETBYTELEN))) {
          return IMAGE_BMP;
     }
     if( (0 == strncmp(firstBit, PNG_FIRSTBIT,   GETBYTELEN)) &&
          (0 == strncmp(secondBit, PNG_SECONDBIT, GETBYTELEN))) {
          return IMAGE_PNG;
     }
     if( (0 == strncmp(firstBit, GIF_FIRSTBIT,   GETBYTELEN))   &&
          (0 == strncmp(secondBit, GIF_SECONDBIT, GETBYTELEN))   &&
          (0 == strncmp(thirdBit, GIF_THIRDBIT,   GETBYTELEN))   &&
          ((0 == strncmp(fifthBit, GIF_FIFTHBIT1, GETBYTELEN))   ||
          (0 == strncmp(fifthBit, GIF_FIFTHBIT2, GETBYTELEN)))) {
          return IMAGE_GIF;
     }
     if( ((0 == strncmp(firstBit, TIFF_FIRSTBIT,    GETBYTELEN))  &&
          (0 == strncmp(secondBit, TIFF_SECONDBIT,  GETBYTELEN))) ||
         ((0 == strncmp(firstBit, TIFF_FIRSTBIT2,   GETBYTELEN))  &&
          (0 == strncmp(secondBit, TIFF_SECONDBIT2, GETBYTELEN)))) {
          return IMAGE_TIFF;
     }
     if( (0 == strncmp(thirdBit, ICO_THIRDBIT, GETBYTELEN)) &&
          (0 == strncmp(fifthBit, ICO_FIFTHBIT, GETBYTELEN))){
          return IMAGE_ICO;
     }
     if( (0 == strncmp(thirdBit, TGA_THIRDBIT, GETBYTELEN)) &&
          (0 == strncmp(fifthBit, TGA_FIFTHBIT, GETBYTELEN))){
          return IMAGE_TGA;
     }
     if( (0 == strncmp(thirdBit, CUR_THIRDBIT, GETBYTELEN)) &&
          (0 == strncmp(fifthBit, CUR_FIFTHBIT, GETBYTELEN))){
          return IMAGE_CUR;
     }
     if(0 == strncmp(firstBit, PCX_FIRSTBIT, GETBYTELEN)){
          return IMAGE_PCX;
     }
     if( (0 == strncmp(firstBit, IFF_FIRSTBIT,      GETBYTELEN))   &&
          (0 == strncmp(secondBit, IFF_SECONDBIT, GETBYTELEN))   &&
          (0 == strncmp(thirdBit, IFF_THIRDBIT,   GETBYTELEN))   &&
          (0 == strncmp(forthBit, IFF_FORTHBIT,   GETBYTELEN))) {
          return IMAGE_IFF;
     }
     if( (0 == strncmp(firstBit, ANI_FIRSTBIT,   GETBYTELEN))   &&
          (0 == strncmp(secondBit, ANI_SECONDBIT, GETBYTELEN))   &&
          (0 == strncmp(thirdBit, ANI_THIRDBIT,   GETBYTELEN))   &&
          (0 == strncmp(forthBit, ANI_FORTHBIT,   GETBYTELEN))) {
          return IMAGE_ANI;
     }

     free(imagebuf);
     imagebuf = NULL;
     fclose(fd);
     return NULL;
}

char *JudgmentImageByName(char *Filename)
{
     assert(Filename != NULL);

     char *TypeName;
     char *pStart = NULL;
     char *qEnd = NULL;
     char *name;
     int i = 0;

     name = (char *)malloc(strlen(Filename) + 1);
     memset(name, 0, sizeof(name));
     strcpy(name, Filename);
     pStart = name;
     qEnd = pStart + strlen(name) - 1;    
     reserve(pStart, qEnd);

     TypeName = (char *)malloc(strlen(name) + 1);
     memset(TypeName, 0, sizeof(TypeName));
     sscanf(name, "%[^.]", TypeName);            // 取「.」前面的部分
     pStart = TypeName;
     qEnd = pStart + strlen(TypeName) - 1;
     reserve(pStart, qEnd);
    
     for(i=0; i<12; i++){
#if 0
          if( (0 == strncmp(TypeName, MImagesType[i], strlen(MImagesType[i]))) ||
               (0 == strncmp(TypeName, LImagesType[i], strlen(LImagesType[i]))))       // 只匹配部分字符串，致使出錯。
               return MImagesType[i];
#endif
          if( (0 == strcmp(TypeName, MImagesType[i])) || (0 == strcmp(TypeName, LImagesType[i])))
               return MImagesType[i];
     }    

     free(name);
     free(TypeName);
     name = NULL;
     TypeName = NULL;
    
     return JudgmentImageByDate(Filename);
}

int main(int argc, char *argv[])
{
     int res = -1;
     char *imageType;

     if(argc < 2){
          printf("usage: %s <imagefilename>\n", argv[0]);
          exit(1);
     }

     imageType = JudgmentImageByName(argv[1]);

     if(!imageType)
          printf("not a picture!\n");
     else
          printf("%s\n", imageType);

     return 0;
}