c - 如何将 for 循环中的整数作为十六进制值输出到文件

Question

我试图用一些 C 代码创建一个 .pam 图像，但 fwrite 函数只将对应的 ASCII 码写入文件，而不是十六进制值。

文件的头部需要是 ASCII，实际的图像数据需要只是 rgb 和 alpha 的十六进制值。

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

int main() {

    FILE *out;

    out = fopen("C:/Users/entin/Desktop/write.pam", "wb+");

    if (out == NULL) {
        printf("Unable to access file.\n");
    } else {

        //everything concerning the head

        //buffer the head to not get an overflow
        unsigned char headbuf[100];
        sprintf(headbuf, "P7\nWIDTH 255\nHEIGHT 255\nDEPTH 4\nMAXVAL 255\nTUPLTYPE RGB_ALPHA\nENDHDR\n");

        //reduce head to nessesary length so it dosent output useless NULL's
        int len = strlen(headbuf);
        unsigned char head[len];
        sprintf(head, "P7\nWIDTH 255\nHEIGHT 255\nDEPTH 4\nMAXVAL 255\nTUPLTYPE RGB_ALPHA\nENDHDR\n");

        //write head to file
        fwrite(head, sizeof (head), 1, out);


        //initiating pixel values
        unsigned char buf[8];
        int r = 0; //AA
        int g = 0; //BB
        int b = 0; //CC
        int a = 255; //DD

        //for now just change the red and green values
        for (r = 0; r <= 255; r++) {
            for (g = 0; g <= 255; g++) {

                //coppy pixel data to buffer
                sprintf(buf, "%02X%02X%02X%02X", r, g, b, a);

                //write buffer to head
                fwrite(buf, sizeof (buf), 1, out);
            }
        }

    }
    fclose(out);
    printf("fin");
    getchar();
    return (EXIT_SUCCESS);
}

它输出我想要的头部，但像素值也写在它们的 ASCII 值中

它输出 ENDHDR\nAABBCCDD

作为。45 4E 44 48 44 52 0A 41 41 42 42 43 43 44 44

它应该像这样输出:45 4E 44 48 44 52 0A AA BB CC DD

Answer 1

我修正了我的代码，只是将值写成对应的 ASCII 码。

这里是固定代码

#include <stdio.h>
#include <stdlib.h>

int main() {

    FILE *out;

    out = fopen("C:/Users/entin/Desktop/write.pam", "wb+");

    if (out == NULL) {
        printf("Unable to access file.\n");
    } else {

        //head
        fprintf(out, "P7\nWIDTH 255\nHEIGHT 255\nDEPTH 4\nMAXVAL 255\nTUPLTYPE RGB_ALPHA\nENDHDR\n");

        //initiating pixel values
        int r = 0; //red
        int g = 0; //green
        int b = 255; //blue
        int a = 255; //alpha

        //for now just change the red and green values
        for (r = 0; r <= 255; r++) {
            for (g = 0; g <= 255; g++) {

                //call the numbers as theirr ASCII counterpart and print them
                fprintf(out, "%c%c%c%c", r, g, b, a);

            }
        }

    }
    fclose(out);
    printf("fin");
    getchar();
    return (EXIT_SUCCESS);
}

这是第一个结果