gcc warning: implicit declaration of function `f2c_generate_note01'

I have a warning from gcc compiler, which I don't know the reason of it.
Can anyone help? The warning is:
- warning: implicit declaration of function 'f2c_generate_note'

The code is as below:

struct elf_note
{
int namesz;
int descsz;
int type;
char name[8];
};

int f2c_dump_core(const char *name, struct crashdump_foc_t *foc)
{
int file;
struct elf_note *note01;

if ((file = open(name, O_WRONLY | O_CREAT, 0777)) == NULL)
{
printf("can not open core file: %s\n", strerror(errno));
return -1;
}

f2c_generate_note01(&note01);

if(lseek(file, 116, SEEK_SET) == NULL)
{
printf("seek note01 failed: %s.", strerror(errno));
return -1;
}

if(write(file, note01, sizeof(struct elf_note)) == NULL)
{
printf("write note01 failed: %s.", strerror(errno));
return -1;
}

close(file);
}

int f2c_generate_note01(struct elf_note *note)
{
note->descsz = sizeof(struct elf_prpsinfo);
note->type = 3;
strcpy(note->name,"CORE");
note->namesz = sizeof(note->name);
}

The role of subfunction "f2c_generate_note01" is to fill the struct elf_note.

And the role of function "f2c_dump_core" is to write the elf_note into a file.

When posting code, you need to use code tags. See here for what I am referring to. Here is your code with some indentation (which is preserved by using code tags):

Code:

struct elf_note {
    int namesz;
    int descsz;
    int type;
    char name[8];
};

int f2c_dump_core(const char *name, struct crashdump_foc_t *foc)
{
    int file;
    struct elf_note *note01;

    if ((file = open(name, O_WRONLY | O_CREAT, 0777)) == NULL) {
        printf("can not open core file: %s\n", strerror(errno));
        return -1;
    }

 f2c_generate_note01(&note01);

    if (lseek(file, 116, SEEK_SET) == NULL) {
        printf("seek note01 failed: %s.", strerror(errno));
        return -1;
    }

    if (write(file, note01, sizeof(struct elf_note)) == NULL) {
        printf("write note01 failed: %s.", strerror(errno));
        return -1;
    }

    close(file);
}

int f2c_generate_note01(struct elf_note *note)
{
    note->descsz = sizeof(struct elf_prpsinfo);
    note->type = 3;
    strcpy(note->name, "CORE");
    note->namesz = sizeof(note->name);
}

As for the warning, try using some function prototypes. This ought to fix your trouble.

thank you for your correction. This is my first time post here, so I don't familiar with the rule. Next time I will pay attention to this problem